Well, I just got off the phone first with T-Mobile and then with Motorola.
T-Mobile claims that the RAZR V3t cellphone does not support EDGE, but because I've had it since January 3, which is a few days longer than the 14-day "buyer remorse" period, they won't take it back.

The Moto web site says that the phone does support EDGE, and the Moto Data Customer Support Rep confirmed that it supports EDGE.

I have the unlimited data plan, which I've had for a year, and I got only GPRS speeds with the V3 I used last year, but I "upgraded" to the V3t based on the Moto web site, plus oral representations from the T-Mobile rep three weeks ago that it supports EDGE. Of course, I have nothing in writing from him, and the T-Mobile web site is silent on the subject.