I was wondering what at&t's most used coverage bands are here in the u.s. is it 850/900? I ask as I understand that an unlocked gsm phone has to be quad band to work on at&t's network. What I'm asking is will an unlocked triband gsm phone work on at&t if it doesn't have the 850mhz band? Does at&t use this band for most of thair coverage here in the u.s.?