When Google was going to pull the plug on XMPP (May 2014), I went looking for a VOIP service to use with my Obi. Anveo had a ridiculous call plan and rate page - I had to call them to make sense of it. In the end I couldn't figure out if I could get a fixed monthly rate for both in and outbound, so I kept on looking.
Vestalink showed up with a simple rate structure. I bought it and not only has the technical quality always been good, but the support is really excellent. So, unlike many in this thread, I have praise for them. (And yes, I realize this has nothing to do with their new ATA offering).