Don't plan on buying a phone designed for AT&T's 4G LTE network and being able to use it with Verizon, or vice versa. LTE stands for Long Term Evolution and is the standard for 4G high-speed mobile data transfers currently being used by Verizon and MetroPCS. However, AT&T plans to get in the LTE game later this summer, with its first LTE phone due out by the end of the year.
LTE uses SIM card technology, something that AT&T, T-Mobile, and almost all international carriers have been using for decades. It works by embedding all the pertinent data - your phone number, calling plan, network information, etc - onto the card.
That card is then, theoretically, interchangeable. So if you have an AT&T SIM card, you'll be able to put it in a T-Mobile phone, as long as the latter phone is unlocked.
However, Verizon is used to running on a different kind of mobile infrastructure where all of that information is stored to the hardware of the phone itself, not on an external card. The transition to a SIM card system is new to the carrier.
Because of the way SIM cards have been used up until now, it would be reasonable to assume that since Verizon LTE phones now use SIM cards, they'll be part of that great, flexible ecosystem.
However, PCMag.com reports that Verizon is using a special kind of technology that prevents anyone from using a SIM card from any other carrier on its LTE phones, and likewise also prevents its SIM cards from being used on a phone from any other carrier.
"The result is an incompatible welter of devices, likely to continue long into the future. If you're dreaming that LTE would allow one device to work on several U.S. networks, dream on," wrote PCMag.
In other words, even though it's now using more flexible technology, Verizon worked specifically to ensure it is as inflexible as it always has been.