I have the exact opposite experience in NYC with Cingular and T-Mobile. Having had T-Mobile for four years, I rarely had a dropped call or network busy signal. With Cingular it happens virtually daily. Same problem here with Cingular billing too.
If I had a choice I'd go with a Motorola Q from Verizon, if I had to have a Blackberry I'd still go with Verizon. Verizon will allow you to tether at EVDO speed for $15/mo extra. Cingular is $30 for EDGE (about 5-10x slower). Not sure about T-Mobile, but the fastest they offer is EDGE. You need to check in your area about the service providers coverage and quality, try www.howardforums.com
and use the trial periods.
As for the 7290, I'd pass. I had it for a year and didn't like it. You lose the speaker phone but it is built better and has a better battery. On the downside, I found the earpiece to be too low to be useful on a street. Car and home/office were passable, barely. The screen and EDGE also are big pluses for the 8700.