4:05 PM -- It seems pretty clear that the Apple Inc. iPhone 5 will be one of the first real stress tests of new 4G Long Term Evolution (LTE) networks in the U.S.

Apple has shifted over 2 million of the new phones in pre-sales before they actually arrive in stores Friday. This makes it the fastest-selling iPhone Apple has ever introduced.

It should also make things interesting for AT&T Inc., Sprint Nextel Corp. and Verizon Wireless as the device quickly becomes widespread. The iPhone 5, with the possible exception of the Samsung Corp. Galaxy S III, will be the first mass-market 4G LTE smartphone in the U.S.

For instance, Verizon said it sold 2.5 million LTE Android smartphones all-told in the second quarter. The iPhone seems likely to beat that number handily, given the pre-sales totals.

So, millions of people are going to be switching these devices on from day one and downloading audio and video over 4G LTE. Operators are also now allowing FaceTime video chat over 4G rather than restricting it just to Wi-Fi. (See Open Internet Groups Slap AT&T in the FaceTime.)

We know that the iPhone 5 is going to be a data hog from day one. We just don't clearly know how the launch will affect fledgling LTE networks in the U.S. yet. (See What We Mean When We Say '4G'.)

At the least, I would expect to see complaints about the lack of LTE coverage -- particularly from AT&T and Sprint -- start to increase with the launch of this phone.

In fact, both operators are racing to cover 100 major U.S. markets with the new 4G as soon as possible, but they can't hope to match Verizon's 371-market 4G footprint anytime soon. (See iPhone 5: Which 4G Carrier to Pick?)

— Dan Jones, Site Editor, Light Reading Mobile