Yeah, your account at Verizon will tell you how much data you are using via your phone. Just log in. Usually it is about a 5 day lag.
When tethering, the Verizon Access Manager will let you know how much data you are using. I used about 1G last month. Of course that is with basic surfing, chat rooms, IMs, emails, streaming of video clips and a few free software programs. When I had comcast modem I would stream Sirius about 20 hours a week. According to Verizon, an hour of streaming can run you about 100MB or in my case 2GB a week or 8BG a month alone. So needless to say I do not stream Sirius on my pc anymore
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But 5GB is alot if not streaming. Just watch your data...
Trent