KilroyWasHere,
I am in some what the same boat. I have 15 handsets, our voicemail runs on a 486 running Dr.Dos. We have low call volumes which is what makes 3cx appealing.
You really have two options, Take a couple of months and learn as much as you can about phone systems or hire a 3cx consultant to assist you. Your needs are going to be much different than mine. Asking for others opinions on what is the best option for a dial tone provider is a good start, but to go with another's recommendation without fully understanding the technology may not go so well.
Many business rely on their phones, if you sell the execs on replacing your system and the project fails, then you failed
. So sometimes its best to hire a consultant. They are always easy to blame.
VIOP Providers can often offer the most cost savings, but keep in mind you are sending your voice over the Internet, where you may get no Quality of Service. Thank goodness for Net Neutrality in the US.
Traditional providers (ATT, TDS, MaBell) can often reduce their costs if your willing to sign a commit of a few years. They also have different methods of service, (POTS, Trunks, PRIs). You will need to know the difference in order to decide what best fits your needs.
Your first step should be to diagram out your phone system as to how you want it to work, not how it works now. Give yourself a visual representation to reference.
Read the documentation, twice, then install the demo. Have fun and play with the settings. Its the best way to learn. You can setup a call centric number for less than $20/month to test.
3cx is not an open source project, so keep in mind that it may be a good idea to maintain both Upgrade insurance and Tech support maintenance on your software.