I've got a few VoicePulse connect (connect.voicepulse.com) trunks working well with my own PBXiaF installation. I had used their FreePBX module, and it worked; however, the module no loger installs IAX2 connections - only SIP. SIP should have been fine with my public IP, but alas, no. After a day or so, I had repeated instances where my registrations would fail. A quick reset would fix it, but that fix was temporary and the problem persisted. I never have that problem with IAX, so I simply ditched the module and just set up the trunks manually. It's been working great.