I'm new to Verizon. I ditched Sprint like I told all my friends I would as soon as the new iPhone came out because of poor coverage at my new house and no attempts to actually make it right by Sprint. All that as a preface to say, I don't know exactly how their billing system works just yet.
I got the 4S on launch day in store...end of the day actually, which suprrised me...and activated it. All was well and still is, aside from less than desirable data speeds where I work, but that's still blazing compared to my old Blackberry on Sprint. I'm not a power data user or anything (I got the 2GB data pack), as I just check my email throughout the day every now and then and do the occasional Facebook browsing and read news at lunch. In the 2 weeks and a couple days since I got the phone, I've racked up 329MB or so of data usage according to the VZW website (which is also about a day behind). However, on my phone the cellular usage adds up to only 263.9MB.
My question is, how accurate is the counter on iPhones for cellular data usage? Is the VZW counter accurate or are they overestimating? There are also a few odd instances where I was clearly at home due to the time of night it was, which means I was on wifi, and there would be 7MB of data usage (according to VZW website) a couple different times and much smaller amounts other times. While on wifi, mind you. Found that odd. Obviously I'm not in danger of going over the 2GB plan I have with either of those numbers, but the 60MB or so discrepancy between the phone's usage numbers and VZW's could make or break me at some point.
I was told: "You should always go by the number on My Verizon" and "We try to update that as soon as possible, sometimes it can be on a 24 hour delay." Hope that helps.