nellyala :
thank you, you are right and i agree with you but i checked websites of at&t and t-mobile. they have lists of compatible phone names and informations but they don't mention " xperia go" so I'm not sure yet, does it work in us or not!
at&t Has emphasized, phones must be:
Operates on GSM network
Operates on 850/1900 MHz bands
Unlocked - not programmed to work exclusively on a wireless network other than AT&T
and my " xperia go" is precisely this but its name isn't in the list of compatible phone names.
First of all, is this the phone you are talking about?
http/www.gsmarena.com/sony_xperia_go-4782.php
If it is, it should work with AT&T and T-Mobile's network. For GSM (voice and text), it will work, since AT&T uses 850 and 1900 MHz frequency, and T-Mobile uses the same. Your phone have the right frequency bands to support them (850, 900, 1800, 1900 MHz). But if you want to go 3G or 4G network, it may not work. Since there are two models according to the link I posted, ST27i, and ST27a. ST27i has HSDPA (3G network) 900 and 2100 MHz frequency band, which will not work on T-Mobile and AT&T. If you own the other model, ST27a, which has HSDPA (3G network) 850, 1900 and 2100 MHz frequency band, it will work on both carriers. Hope this helps.