I noticed the following:
US G1, unlocked, I live in Switzerland, Europe.
When I start application, I can select google talk, msn, a.o.
When I choose MSN, I can enter my userid and pass. Then he tries to connect. After a few seconds there is a message that tells the following:
Unable to sign in to the MSN service. Please try again later. Detail: Sorry, the phone number cannot be read from your SIM card. Please contact your operator.
So I think he connects to some TMOBILE server and there something he wants to do. Perhaps that's the reason why they have token MSN from the UK phones, because they are not able to connect to the US TMOBILE servers or perhaps the US servers dont know about the numbers used in UK.
Just an idea

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