T-Mobile Blocks SIP Protocol Transmissions on port numbers 5060 or 5061
This is a well known problem with t-Moble since firmware version 27.x and I have been trying to reach out to them for nearly two months to get this resolved .. see here https://support.t-mobile.com/thread/137563
We are moving all our business lines off of t-mobile back to verizon because of this and I suggest you do the same so they can learn to stop blocking SIP ports on their network.