I visited Belarus during the first 5 days of the
6-week visa free period, and using a British credit card I topped up my existing MTS SIM card
via credit card online with the negligible amount I needed for 500MB of data. I am really impressed with MTS.
One thing I did notice on this visit was that all SIP seems to be blocked, both on MTS and via non-mobile internet connections such as residential broadband. I also tried MegaFon's
MultiFon service, which likewise uses SIP, but that was blocked too. Other VOIP services like Skype and FreeVoipDeal's proprietary app worked fine.