REPRODUCIBILITY (% or how often): Always
BUILD ID = OS VERSION (Settings > About product): 126.96.36.199
HARDWARE (XA2, X10, X10 II, …): Xperia 10 II dual SIM
UI LANGUAGE: English
The sound quality when calling or receiving calls on roaming is very, very poor. Sometimes so weak that you cannot hear the other person. Sometimes with so much noise that you can not hear for that reason.
(And sometimes the sound quality is good for half a minute to 1 minute, but never for longer then that.)
This is when not using a headset, but using either the loudspeaker, or using it without the loud speaker.
The sound quality with a wired headset is quite OK - but has a noise to it.
The sound quality using Bluetooth is absolutely superb. Best of all phones I have used.
When not on roaming the sound quality is excellent.
I have tested this on 2 x Xperia 10 II dual sim white, european version and 1 x Xperia 10 II dual sim blue, Hong Kong version.
All with the same result.