:: Unlocked AT&T Xenon to T-Mobile :: IM Server Address

 I have an at&t branded Xenon, it's unlocked fine for use with my T-Mobile SIM. The problem is my IM Messenger, I can receive txt and mmtxt fine. But~

I can't login to my Windows Live account, the at&t server address is msn2.cwmim.com :1175

I need to *change* it to T-Mobiles server : http://wirelessvillage.msn.t-mobile.com :4705

But the area the address is shown doesn't let me edit it. And there's no menu in the top right that lets me edit it anyway.

Is there anyway to change this, or is it impossible to set the address, frustrating I can't change the settings.