mobile

Hi All

I have an ex T-Mobile HTC HD2 running windows 6.5 and connected to O2.
Mostly everything works fine except . . . . .
When I try to download an MMS message the phone tries to use the T-Mobile network and as this is not set up, it doesn;t work.

It tries to use t-Mobile even when connected to wifi
I have tried getting onto the network manager but all the T-Mobile settings are greyed out. and there is no option to delete the entry (edit, press and hold gives no options).
Network manager is set to use O2 (Connect to internet and Private network)

So, please, how do I get rig of T-Mobile and default to O2.
I presume it some registry hack?

TFAI