Compared to CallRail the UI is very complicated. Too many different menus and windows to set things up.
Missing key features in the lower plans. I could not use simultaneous calling followed by voicemail if no answer on my plan and would have to upgrade to get this feature.
Unethical practices - I ported a few phone numbers away from CTM but was still charged for them even after they had been moved to the new provider because I did not read the fine print that you have to release the numbers in CTM after they have been transferred. I obviously complained about being charged for numbers that were no longer with CTM, but was told that this was there policy and it was my fault for not releasing them.
Average customer service. I have to admit that they did resolve all my issues, even though many times not the result I was looking for. Usually took a few days for them to get back to me though. Have previously worked with CallRail and they had awesome service. Are now with AvidTrak and they too have awesome service (although not as good UI as CallRail).
Price plans do not include any phone numbers or minutes like other providers so they end up being more expensive in many cases. CallRail unfortunately only include local numbers and minutes in their plans and I needed toll-free so didn't work out for me. AvidTrak is a lot less expensive.
CTM will likely do what you want, I just recommend you go in with your eyes open and make sure you release those numbers if you cancel or port them away or you will be stuck paying for them.