I just bought my 3G usb modem from Viettel today. 780,000 VND for the usb modem. 50,000 VND monthly charge, 65 VND per mb. You can recharge your account like any cell phone in Vietnam, no bills. Initially I got up to 2.92 Mbps downloads with Speakeasy in the US. Not bad. Faster then wired.
Does this modem also work under Linux ?
Unfortunately no. The software only runs in Windows and Macs.
Just the thing for me when I go back there. Those things and the service packages that come along with them can cost an arm and a leg here in the US.