Can I use a T-Mobile Sidekick if I am with AT&T?

Question

I'm with AT&T, will be for a long time, but I was wondering since they are both GSM networks if i could just buy a Sidekick and use my current sim card in it

Answer 1

If you got an unlocked Sidekick, you could use it with an AT&T SIM card for phone and texting, but you wouldn't have web browsing or email as full Sidekick service is only available from T-Mobile.