hehe. that was a while ago, but I still use it in the car whenever on a long drive.
I use verizon's family plan which includes national access, meaning you can call from almost anywhere in the nation without roaming fees. Ontop of that, after 9pm (monday - friday) access is free, in terms of not using any minutes, until 7am. And ALL weekend is free as well. As for having it on 24/7 durring the weekday, you'd have to get some other plan. Otherwise durring the day you'd burn through your minutes pretty quick. I believe bluetooth, in theory ;-) , gets around 700 kbits/sec. But that's just the speed you are connecting to the phone; the speed to the phone network is the real speed test. Using Verizon's 1X data network you can connect at 114Kbits/sec. I get anywhere from 5 - 12 kilobytes/sec download speed, so not too bad for using your phone.
While going through the desert in vegas I got pretty good signal bars on my v710, so my internet connection was pretty reliable, in terms of not dropping a download or chat session. I imagine this is because there just wern't a lot of obstructing objects near the road; the desert was pretty open on both sides of the road. Although I didn't do any official benchmarking, I remember loading webpages may have seemed a bit slower driving then siting in the hotel, so perhaps moving in the car did affect the signal somewhat. I also remember that I needed to download AIM for my laptop, and got around 5kbytes/sec while in the car. Whereas while I was sitting still in the hotel, the max download speed I got was 9-12kbytes/sec. However, the max speed in the hotel could be because I was in the city and not on the road, so I had better line of sight with the cell tower. My point is that going 70mph in a car probably does affect the connection speed, but I don't want to rule out this being a line of sight signal issue. No real scienctific testing here, just some observations.
I was chatting on AIM with a friend and browsing the web for a good couple of hours without any disconnects while in the back seat. I didn't get a chance to watch the signal every minute to confirm if the slow webpage loading was due to low signal, but for the most part the connection was reliable, up until I started going through the border on Arizona, where you have some mountain/hills very close to the road, plus you're really far away from any major city. Once in that area, it did seem to slowdown even more, and disconnects would happen. So really is just depends where you are driving; going through the desert in vegas probably isn't an everyday test for people since most people are going in and out of cities, mountain areas, etc, with much more obstructing objects. But if you can count on your travel route being pretty standard with no major obstructions near the road and have a decent signal, then going 70ish in the car shouldn't cause your internet connection to be so unreliable that you can't maintain a connection. As for battery, I get maybe 2 hours with my motorola v710, so when on a drive I leave it pluged into the car.