HTC One Mini - Turn on international network from within the phone?

[Mellfee]

I've got a new One Mini which I only got a few days ago, just before leaving for America. I didn't get chance to make sure it would work outside the UK and since getting here I can't get it on to a network. AT&T and T-mobile are both available but it just comes back saying sim card won't connect.

I just tried registering with Three online (my UK network) but they text the password to you so I can't register.

Is there a way to set it up from the phone?


Thanks