well it's none other than MOBITEL. but sometimes their 3G signals sucks.
Yes, Some 3G Enabled towers can`t switch our phone to 3G network automatically... Phone stays in GSM network.. Need to Go to well worked 3G area, let our mobile to switch to 3G, turn our offline profile, and come back to the corrupted 3G tower, then turn on the any other network enabled profile... Then it works well..
Sometime, Sucks!