While these types of cancellations can be difficult to foresee on an individual basis, we would expect a reversion to the mean, if you will, in line with broader trends of roughly 4% to 6% we have experienced over the last several years. While we believe the demand for our wireless services will continue to decline on a secular basis, as reflected in declining pager units and service, we are hopeful that our focus on pricing and other initiatives, like the Gen-A pager, will continue to further offset revenue lost through pager unit decline. Given a unit churn of 4% to 6%, we do not believe future incremental pricing increases and higher ARPU products, like the GenA pager, will be sufficient to completely offset revenue decline realized from net unit loss.
This is further reflected in our updated financial guidance, which I will walk through shortly. Turning to software revenue in 2023, license revenue of $8.7 million was up by more than 21% from 2022. Maintenance revenue totaled $37 million and was up slightly from the prior year. As we have discussed in previous quarterly calls, we expect continued progress on our product development roadmap will lead to further growth of our operations bookings in the coming years and maintenance revenue along with it. With that said, the performance of our maintenance revenue has exceeded our expectations. When we initiated the strategic pivot in early 2022, we were hopeful for a return to maintenance growth by 2025; so to see that happen in 2023, two years sooner than originally anticipated, is just tremendous.
Professional services revenue was a strong $14.7 million for 2023 versus $12.6 million in 2022 and continued to accelerate throughout 2023. We are seeing further sustained improvement in resource utilization, delivering on our internal initiatives to better align total resources with our backlog and driving a higher rate of margin in net cash flow. We hired several service professionals in the second half of 2023 to meet our current backlog needs and to support new professional services opportunities such as Spokes Value Added Service Consulting Solutions, where we partner with customers to help them maximize the power of the software products and solutions they have purchased from us or from other vendors. Full year 2023 adjusted operating expenses, which excludes depreciation, amortization, and accretion, and severance and restructuring costs, totaled $112.7 million, down nearly 9% from the prior year.
Increases in research and development were largely timing in nature, with reductions in technology operations driven by our normal practice of cost reduction in relationship to declining paging revenues. Slight increases in selling costs, which primarily result from the higher bookings production, were more than offset by savings in G&A, which continues to see year-over-year benefit from our cost-saving initiatives. As I mentioned in our last quarterly earnings call, company-wide salary increases went into effect in late fourth quarter of 2023. As a result, we expect our expenses will be approximately $1 million higher in 2024 on a comparable basis. Additionally, as discussed in our last quarterly earnings call, we expect to hire additional sales resources in 2024 and anticipate sales and marketing costs will continue to marginally increase as a result.
These resources will support our robust sales pipeline and generate additional sales activity as we look to extend the sales growth we have achieved over the last two years. Lastly, as Vince pointed out earlier in the call, adjusted EBITDA was a record $30.3 million in 2023, up more than 100% from $15 million in 2022, reflecting the progress made to date with our strategic pivot. Moving on to guidance for 2024, we have provided estimates for revenue and adjusted EBITDA. The provided ranges reflect our confidence in carrying the momentum from 2023 into this year. As a reminder, the figures I’m going to discuss today are included in our guidance table in the earnings release. In 2024, we expect total revenue to range from $136 million to $144 million.
More importantly, this represents the second consecutive year that we expect to grow consolidated revenue from the prior year based on the midpoint of our guidance, with a nearly 4% annual growth rate at the high end of our guidance. Included in the 2024 guidance, we expect wireless revenue to range between $72 million to $75 million, reflecting low single-digit attrition at the midpoint of the range. We expect recent trends to continue and stabilize during the year. Software revenue is expected to range from $64 million to $69 million in 2024, with the midpoint implying total software revenue growth of more than 5% and nearly 10% annual growth at the high end of the guidance range. Lastly, our adjusted EBITDA guidance for 2024 is $27.5 million to $32.5 million, improving on our strong performance in 2023 at the midpoint of the guidance range when considering the additional costs we expect to incur in 2024, resulting from the aforementioned salary increases, with opportunity for high single-digit growth at the high end of the guidance range.
With that said, I will now turn the call back over to Vince.
Vincent Kelly: Thank you, Calvin. Before we open the call up to your questions, let me say again how proud I am of our entire Spok team and the results we posted for 2023. It is their efforts and dedication which provides confidence for our outlook and guidance for another strong year in 2024. We are focused on the opportunity in front of us in clinical communications. From a business configuration and strategy perspective, we believe we are strongly positioned to grow our franchise while returning capital to our shareholders. We have a long-term organic growth engine in Spok CareConnect. We maintain a source of strong recurring revenue in our wireless service line. We run the largest paging offering in the world, integrated with our software operations.
We have enhanced our paging platform and user devices to serve our core healthcare customer base. We believe with these two assets going for us, our best financial results are ahead of us and Spok’s future is bright. I’d like to take this opportunity to thank our stockholders for their continued support. I want to assure you that our primary focus remains on generating cash and increasing stockholder value. We are committed to our current dividend and capital allocation policy. I’d also like to tell everybody about a couple of events that Spok’s management team will be participating in over the next few weeks. First, on Monday, February 26, this coming Monday, we’ll participate in the opening Bell Ceremony for NASDAQ at their market site in Times Square.
Next, on March 13, Spok will be presenting at Sidoti’s Virtual Small-Cap Conference and hosting a series of one-on-one meetings with investors. I believe Spok is finally receiving recognition as a top-performing company among its peers and will continue to look for opportunities to tell our story to the investment community and focus on investor marketing activities, though we know the ultimate attraction will come as a result of our consistent and successful business execution. I believe today we’ve provided you an appreciation for some of the great things that are happening at Spok and the market opportunities that lay ahead of us. While we’ve shared our initial guidance with you for 2024, as we did in 2023, we will work to exceed those expectations and we’ll update you each quarter.
As I mentioned earlier in the call, we’ve started the year off strong and we look very much forward to speaking with you again in two months when we report our first quarter results in late April. That concludes our prepared remarks. At this point, I’ll ask the operator to open the call up for your questions. We’d ask you to limit your initial questions to one and a follow-up, and after that, we’ll take more questions depending on how much time we have. Operator?
Operator: Thank you. [Operator instructions]. There are no questions at this time. I would like to turn the call back over to management for closing comments. Oh, actually, we do have one now, and that is from Max Michaelis with Lake Street Capital Markets. Please proceed, sir.
Max Michaelis: Sorry about that, guys. I thought I was in the queue. Two questions from me. Nice guide, solid quarter. First one here is on software revenue for 2024. The high end of the guidance I think I see is 10%. Maybe kind of go through the software revenue. What gets us to that 10% kind of the puts and takes there?
Vincent Kelly: Calvin, you want to take that?
Calvin Rice: Yes, I mean, it is going to be a similar mix to what you saw in 2023. In the last several years, I would not expect a significant change in mix. A big portion of that is going to continue to remain maintenance with those churn levels being critical. From an operational bookings perspective, it is going to be quite a bit of professional services, and that is all going to be glued together with the license component that continues to funnel in. I will say, and I will add to that, in that we have changed our software commissions plans this year to focus on new business and to focus on license, i.e. they make more for selling license and new business. As, license hits revenue much quicker than professional services, and it has got a higher margin associated with it.
We are doing things in the business in terms of the drivers that will incent behavior that will yield to more profitable sales in the future. Our top seven software sales reps this past year in 2023 sold a combined $23.3 million worth of software. That compares to about $12.1 million in 2022 for the top seven sales reps. We are getting more out of each rep, and then what we are getting out of each rep is getting more profitable as we go forward. We are continuing to deliver more product upgrades and enhancements to our solutions and adding functionality, including bacon AI, into our capability with our voice products this year. That is also going to help the salespeople’s job in terms of selling higher margin solutions. I think these are nice, good, conservative estimates we have given you.
We are happy with these estimates, and we are going to work hard to beat them and do even better than that.
Max Michaelis: No, that is great. Then my second one is going to be, if we think about software bookings, and you mentioned there was a push-out in Q4 into Q1, I was wondering if you could quantify the amount that was actually pushed out. Then if we think about bookings for the year, I know you had mentioned you had expected bookings to be above that number of 30.1 for the year. You said you expected it to be well above that 30.1 for the year. Can we see double-digit growth out of software bookings again?
Calvin Rice: Yes, I expect we are going to see double-digit growth out of software bookings again. January was an enormous month. It is the biggest January we ever had in software bookings. You just do not know when that stuff is going to come in. We actually do a lot of work on our pipeline to try to quantify when the pipe is going to come in and when it is going to get delivered. Something can get on someone’s desk and just not get signed, and then you are in a situation where you thought you had the deal and you did not get the deal. We have been working on a formula with our pipeline. Our pipeline is up to about $116 million right now. We added almost $100 million to it in the last year. We want to add up to $150 million this year.
We take that pipeline and we qualify it. The deals that have been closed, essentially, just waiting to launch, we count all of those in our estimate and our projection. We have what we call deals that we qualify in the 90% category. Those are committed deals where we got all the paperwork in, but it is sitting on someone’s desk. Historically, you would think you would get all of those, but you generally only get about 60% of those in that given period. We weight that by 60%. We take the deals that we consider 75% deals, and those are where we have been chosen as a vendor of choice. The bake-off has been done. We have won the bake-off. Paperwork is in process. We are exchanging red lines. We are doing contractual things. That 75% category, we only take about 35% of that.
Then we have a category that is 10% to 50% that is in various stages of early completion. We generally only get about 10% of that. We add it all up and we do our best to try to zero in on exactly where we are going to come from a forecast perspective. In the fourth quarter, it just happened that some of that calculation was wrong and it slipped into January. We will continue building this algorithm. We will continue building this model and this pipeline analysis and try to get better at forecasting that in the future. We expect to have a good year this year. We expect to do a lot better than we did last year. We are already seeing that in the early returns.
Operator: Our next question is from David Wright with Henry Investment Trust. Please proceed.
David Wright: Hi. Good afternoon. To follow up on Eric’s questions and your comments about the sales force, can you talk a little bit about CoreConnect hosted, how that is going to ramp over the course of the year? Also, it is really interesting when you talk about the sales force, the incentives. Are you selling hosted by region, same sales force, dedicated sales force? Anything you can say?
Vincent Kelly: Yes. Here are great questions. I will go in reverse order. It is a dedicated sales force we brought on just to focus on hosted. We had one up and running last year. We sold one in January. We have the paperwork for three others we are working on right now. It is starting. Understand, in that customer size stratification that Michael was walking through a little while ago, we are targeting the hosted at the very small hospitals. Some of these locations have 100 beds or less. It is not a big ticket item. It might be a $50,000 ticket. Over multiple years, it is not a $5 million ticket like we got in the second quarter of last year. They are small. They are building recurring revenue. It is wonderful from a subscription standpoint.
That is a new offering for the company. It is really to allow these smaller customers that historically have not been able to afford a very expensive PBX and a very expensive premise-based solution that has multiple file servers and requires professional services to install. Is the hosted solution as robust as some of our very mature standalone solutions that are premise-based? No, but it is certainly functional for a smaller institution. We are already starting to see it start to take off.
David Wright: Is it an incrementally significantly higher margin piece of business?
Michael Wallace: This is Mike. I think over time, once we have some critical mass, it should be something that is a fairly easy installation. The other thing that is interesting about this model is it is different from the revenue recognition related to our on-premise business. It is a subscription model at the end of the day. So, there is a subscription revenue stream that will come from this. As I said in my remarks, you saw that we have very, very little penetration in that small market, the under 200 beds. So, this really gives us an opportunity that we have never had before to attack them. So, this is going to take a little bit of time to roll out, but it is something that we think has legs ultimately.
Operator: [Operator instructions] Our next question is from George Melas with MKH Management. Please proceed.
George Melas: Thank you, operator. So, my question — good afternoon, guys, and great job in 2023. My question was basically exactly the same as the previous caller. So, I will try to elaborate a little bit. Maybe how many salespeople do you have that are dedicated to hosted? Do you also go through channels, or is it all going to be direct? And how do you handle the fairly high cost of sale on a percentage basis, given that it is a pretty small ticket item?
