We took a weekend trip to our summer place "up North" (about 20 miles southeast of Traverse City). This was a prime test of the speed of the Pre and also the iPhone 3GS. How far would the 3G networks extend? In the past, I've had pretty good Sprint service on the Treo 700p and even ok on the old 600 (almost 5 years ago!). This is important, since we have no phone or internet service at the old 1911 farmhouse; even electricity was an add-on!
It didn't take long to find out. On our drive, just north of Lansing (the other side of I-69) the iPhone dropped off the 3G service and onto Edge. It never recovered all weekend. This is consistent with the AT&T coverage maps. Sprint, on the other hand, has pockets of 3G around most cities and along long stretches of the highways. Over two days I took many speed readings and Web site load times, the Pre ranged from 80-900 kbps; the iPhone from 20-190.
To be fair, at our summer house, both were on 2G in the range of 80-150. This is much better than 2 years ago, when AT&T had no service (phone or otherwise) at all. But overall, Sprint is a more consistent network. There were multiple times when the iPhone wouldn't connect or would drop service. On Sprint, there was only one data dead spot -- southeast of Cadillac along M-115. In that area, only roaming phone service was available.
Bottom line: if you want smartphone highspeed data service in Michigan north of the 3 main metro areas, stick to Sprint, and avoid AT&T.