Along with kicking off iPhone 4 pre-orders, Verizon announced on Thursday that it is now throttling network speeds for the top five percent of its data users. The company is also now using a new data optimization system that compresses images and videos its customers see when Web browsing.

Verizon stated in a memo (PDF), “If you use an extraordinary amount of data and fall within the top 5% of Verizon Wireless data users we may reduce your data throughput speeds periodically for the remainder of your then current and immediately following billing cycle to ensure high quality network performance for other users at locations and times of peak demand.”

Verizon: Now with more throttling

Since iPhone owners tend to be among the heaviest data users on a cell carrier’s network, there’s a good chance many will be subject to Verizon’s new policy after a few weeks of use. They’ll also get to experience lower quality images and video along with Verizon’s other smartphone customers.

“We are implementing optimization and transcoding technologies in our network to transmit data files in a more efficient manner to allow available network capacity to benefit the greatest number of users,” the company said. “These techniques include caching less data, using less capacity, and sizing the video more appropriately for the device.”

Verizon added, “While we invest much effort to avoid changing text, image, and video files in the compression process and while any change to the file is likely to be indiscernible, the optimization process may minimally impact the appearance of the file as displayed on your device.”

In other words, there’s a chance that if you load the same Web page on an AT&T iPhone 4 and Verizon iPhone 4, they won’t look the same.

Verizon’s new policy may help avoid some wireless data bottlenecks, but it may also upset its new iPhone customers expecting the same surfing experience they can get with their AT&T iPhone.

[Thanks to Boy Genius Report for the heads up.]