[F00Fbug]

Callcentric provides a bunch of features for a great price. I ported over my two landlines over 10 years ago and love it. When my mom moved to a new state, I ported her number first so she could keep that number in her new place.

If you're actively managing a large number of users and devices, I had great luck with OnSIP. They're not the cheapest game in town, but their management interface is top notch. They were always innovating and the architecture they disclosed was impressive; very focused on HA and performance.