Open the following ports on your firewall:
- TCP 5060-5061
- UDP 4500 (aka IKE Traversal) – Note: This is the port the call data goes through
Additionally, you may need to let IKE Key Exchange traffic through.
- UDP 500
Other errors:
REG99 – Go to my.t-mobile.com and update your E911 address (even if you previously have)