US telecom titan Verizon on Friday was giving itself the option to slow wireless data feeds to customers gorging on rich digital content streamed to smartphones or tablet computers.

Implementation of the new "network management" tactic came a week before the eagerly-anticipated addition of the iPhone 4 to the cornucopia of devices serviced by Verizon.

Apple's exclusive alliance with AT&T in the United States will end on February 10 when iPhones synched to Verizon's network hit the market.

Verizon began taking iPhone 4 orders early Thursday and halted sales less than 24 hours later because people snapped up all the handsets allocated.

"In just our first two hours, we had already sold more phones than any first day launch in our history," said Verizon Wireless chief executive Dan Mead. "It is an incredible success story."

Verizon maintained that throttling service to customers who devour unusually high amounts of data was intended to make sure that the bulk of users get top performance from the network and was not related to the iPhone.

The telecom carrier estimated that about five percent of its customers fall into the heavy data user category typified by "people who are streaming video all day."

The updated policy gives Verizon the right to choke data flow to heavy users but Verizon expected it would only come into play for someone "using an extraordinary amount of data in a congested area at a congested time."