For those of us for whom the USSD procedure doesn't work because our data cards or modems don't support it, or just because we find the whole procedure way too fiddly, I can thoroughly recommend the current version (1.1.3) of the freebie NetMeter (http://www.metal-machine.de/readerror/), which has been mentioned occasionally in these threads. I've used it for years, and unlike the VC or even generic Dashboard apps it is surprisingly accurate at reflecting exactly how much data you have used and have left, if you set it correctly when you load your bundle. Also useful for checking your speed, keeping data logs and more.
You could of course also load Ginngs' own software which adds a whole lot of additional functionality not found in the generic or provider software, though it isn't very happy with some cards.