At the launch of iPhone 4 on Verizon’s network, Apple’s chief operating officer Tim Cook said that the company would have had to make many design compromises to use the first generation LTE chipsets in an iPhone, and that it therefore decided against a 4G LTE handset.
Although the statement is slightly vague, it probably means that LTE chipsets are a bigger drain on battery, or that engineers would have to increase the size of the iPhone for it to be LTE-enabled. It is clear though that Apple will most likely work on the LTE version of iPhone later, as its first priority was to provide iPhone 4 to Verizon customers in the USA as early as possible.
Verizon’s contenders in the 4G space are AT&T, Sprint and T-Mobile, the last two of which have been in an advertising war of sorts over whose 4G network is fastest. To be precise, Sprint has a WiMax network whereas T-Mobile has HSPA+, both of which offer 4G-like speeds.