That was Verizon direct.
The big charges were from data overuse, but I was careful to monitor my usage, and I'm sure that I was right. At first I suspected Windows XP (or a mailbot or something) was doing behind-the-scenes data transfers, but when we looked at Verizons comm journal and the detail records therein it became apparent that was not the case. And then it started happening on linux. A couple times I used dataservice almost up to the limit and then quit using Vz altogether so that I'd stay below the price threshold, but it didn't work! There was a flurry of weird data transfers just before end-of-billing-cycle and I'd end up owing hundreds again.
Something crooked was going on and I didn't know whether it was Verizon or someone within Vz cheating both them and me.
The only solution was to quit.
I'd like to get a pre-paid datacard that would quit working if I exceeded my pre-pay, but there's no such thing that I know of. I think the cellphone companies are happy to overcharge their customers.