Unfortunately, cell service and satellite feeds are finicky, so not everything worked well in my tests. Traffic reports, for instance, weren't always accurate. On one trip to Costco, the AT&T and Sprint phones reported traffic alerts ahead. We sailed smoothly through the alert because there were no traffic tie-ups; both reports were too dated, despite the fact that they're supposed to occur in real time. Verizon's VZ Navigator was more accurate, as it didn't report any traffic problems ahead.

On another occasion the Sprint reported traffic problems 2 miles ahead but the AT&T said 1.5 miles ahead; the other anomaly was that the Sprint gave the alert a severity rating of one while the AT&T called the same alert a four. In this case, traffic slowed just a little bit, so the Sprint service was on target.

One neat feature: If you're a regular commuter, you'll like AT&T's Commuter Alert. It gives you a way to set up a specific route and have it automatically check the traffic, at, say, 5 p.m., just before you leave work (if you really leave that early).

Considering the Costs

Each vendor has a different way of charging for the data streams--say, downloading maps and doing searches. An average route is about 35kb.