I have a Nexus 5 with Android 4.4.2 on it.
I setup the SIP username/password and it works great to make a call from my home WiFi using the cell phone.

When I use T-Mobile's data connection (LTE or 3G) all I get when I place a call is Ringing on my cell, but the call does not show up on the number I am calling nor does it complete.
I've check to see if T-Mobile might be blocking that traffic and the best I can tell they don't.

Any ideas on why it's not working?

Thanks