I've done everything that you mention yet the phone will not connect. I select sign in, it tries and then nothing.

N900
Address: <ext>@<call manager ip>
Password: <random>

Advanced:

Use for telephone numbers: <unchecked>
Username: <call manager end user name>
Transport: Auto
Outbound Proxy: <call manager ip>
Port: 5060
Discover Public Address: <ticked>
Loose Routing: <blank>
Keep Alive mech: <auto>
Keep Alive period: <auto>
Auto-detect STUN: <ticked>

CUCM 7.1.2

End user already was present - reused

*other call manager settings as standard, but I did select media termination point*

The phone does not register whatsoever.

Any ideas what I am missing?