What's your favorite solution for small VoIP systems? Less than 30 phones?

Greetings /r/networking,

I've been supporting customers with CME for years now. We've always used it for closed networks with a small number of users and generally very little day to day use. Mostly it gets used for other network maintenance.

For example, at a previous job, we setup a VoIP network to all our cellular base station sites. We had a bunch of phones in the office. Generally speaking we only used it to talk to people doing work on the cell sites. Obviously needs to be super reliable when we're doing maintenance. But otherwise is hardly used. No PSTN connections.

I've always used CME because it's quick to setup and easy to maintain. However, I've decided it's time to take a look at other call managers that might fit the bill for very small VoIP networks. My first look will be CME running on a virtual router, a.k.a. CSR1000.

But I also want to look at other call managers that I might not know about. Low cost is nice, but not required. But offline licensing is a must. All the networks I build and manage, like the cell site management, are not connected to the Internet. All our licenses are static and permanent. I never want to risk the integrity of the system security having to pop my call manager on to the Internet to get a license.

I was thinking of taking a look at Asterisk. I remember back in the day when it was the CM of choice for my Linux admin friends.

Does anyone else have any favorites they can recommend? Anything you would stay away from?

Thanks in advance, -Paul