Ясно вече защо е такова качеството при Вивател:

TEFR:
When a call is in progress you can see the speech codec type from this display. When TEFR (Transfer channel Enhanced Full Rate) is displayed as channel type, both the base station and your phone support this better-quality voice codec. A standard Full Rate speech channel will be shown as TFR. GSM networks built in 1990's may contain lots of old base stations that do not support EFR codec. You can detect them by using the Network monitor.

-=MaHLaN=-