Hey,
It's an AT&T purchased in the US. I'm not in Hanoi - too bad for me
Based on the specs, and what I've seen about Viettel & Vinaphone frequencies (I guess), this model should work. Being an AT&T phone, on eof the setting selectors is "greyed out" which won't let me select a network. I'm thinking that may be the hitch. I'm a noob so I don't Know what TopSmart is. Any help appreciated. Thanks.
TopSmart is a cook rom. Don't mind.
So in general, you can call (and text also) but no data connection, right ? In US (or wherever your previous country), data connection still ok, the problem have occured just in time you arrived in Vietnam ? Have you changed
anything in your phone's setting ?
Have you register the 2G/3G service with the mobile network provider (Mobiphone, Viettel or Vinaphone - which you still using) ? - It's importance !
Because you can call, I guest your network setting is alright. Try to go to System setting ~> Wireless and network settings ~> Mobile network and check on the box Data enabled (on top of the screen). Restart your device if required, and then open your browser, connect to google.com for testing.
If it didn't help, please take a screenshot of the Mobile network settings screen and attacht here for more reference.
Best regards.
P/s: please answer all my question for providing me as much information as you could. And finnaly, tell me the name of your mobile network provider in Vietnam you currently using. It could helps.