(AP) -- On the same day it started taking pre-orders for the iPhone, Verizon Wireless started reserving the right to slow down data service for subscribers who consume far more than others.
A document on the company's website said that, starting Thursday, subscribers who sign a new contract for an unlimited data plan - a requirement to buy a Verizon iPhone - are agreeing that the carrier may throttle their data speeds if they use so much data that it slows down service for other users.
Heavy data use from iPhone users has caused congestion and poor service in some places on AT&T's network, but Verizon Wireless spokesman Jeffrey Nelson says Verizon's move isn't related to the launch of the iPhone. The growth in smart phone use in general prompted it, he said.
"This is looking ahead and making sure that our customers get the experience that they expect from us," Nelson said. "We all have seen what happens when a company doesn't manage its network."
Verizon started taking pre-orders for the iPhone from current subscribers at midnight. It starts selling the phone in stores next Thursday. Previously, AT&T Inc. has been the exclusive carrier for Apple Inc.'s iPhone in the U.S.
Verizon isn't planning to slow data speeds for heavy users by default, Nelson said. Where there are few other users who connect to the local wireless tower, heavy data use may not affect others.
Nelson said Verizon won't throttle speeds for subscribers who signed their data-plan contracts before Thursday, nor will it do so for users on limited plans. They pay extra when they use more than their monthly data allotment.
Verizon has said that the unlimited data plan for the iPhone is a temporary measure designed to give it a marketing edge over AT&T Inc., which provides only limited plans for new customers.
All wireless carriers report that a small number of wireless users account for the majority of data use. Video and audio streaming services are typically the ones that push up data usage.
T-Mobile USA already throttles the speeds of some heavy smart-phone users. AT&T doesn't, according to spokesman Mark Siegel.
Verizon also said it reserved the right to "compress" or shrink video feeds to smart-phone subscribers.
The blog Boy Genius Report reported first on the Verizon document.
Explore further: ESPN says Verizon's new FiOS TV packages violate agreements