For one thing, the next version of the is expected to be released this year (probably this summer). For another, AT&T's 3G network, while arguably less reliable than Verizon's -- especially in key markets, such as New York City and San Francisco -- is faster when you have a decent connection.

And there are more issues. The Verizon iPhone doesn't support voice and data operations simultaneously. Plus, competition from -based is fierce, and they're evolving rapidly.

We've been testing the Verizon iPhone 4 at Computerworld. First, let's get this out of the way: Despite numerous reports about differences between the two versions of the iPhone 4, from a user perspective they're virtually identical. The Verizon version lacks a covered SIM-card slot, and the antenna has four dividers instead of three in the stainless steel rim. On the inside, there are several minor differences, the most significant being required for Verizon's network.

In our tests in the greater Boston area, the Verizon phone cleared up the one nagging issue troubling users of the AT&T iPhone: connection strength and reliability. Our testing showed that Verizon's network delivered significantly stronger reception than AT&T's. In one example, we found that the Verizon iPhone was able to grab three bars in Computerworld's gym, which is in the partially underground basement level of our office building. For the AT&T iPhone, this same room was a dead zone.