It will work great on wifi but with digi 3G, i think certain areas only cause..

Digi  surely a hassle with the coverage problem
although I've no problem using Viber on EDGE

but of course for a stable connection when making phone calls
i believe Wifi is better plus it doesn't use up the 1gb digi internet quota

Hi everyone,

I'm excited to announce that according to preliminary results, it seems as though we managed to find and fix the collision problem of Viber with CM7 and MIUI ROMs (and possible the rest as well)
Both these ROMs "change" the device's identity (virtually, of course), preventing Viber from adapting itself correctly to the device's microphone configuration. This is why most of you with ROMs experienced the one-side audio issue.

Anyway - we are working on adding a fix to the new version that will hopefully be officially released next week to Market.

Updates soon,
Viber.