Be careful what you wish for. The iPhone has realized the old promise of the mobile Web. But it's not clear whether the wireless networks can handle the load.

With news that Apple's little cell phone now accounts for more mobile Web traffic than any other device in the US -- and is No. 2 globally -- the issue of whether or not Web-enabled wireless devices will overwhelm cellular and Wi-Fi networks is about to come to a head.

Of course, it's not just the iPhone. Adding to the growing ways to access the Web over wireless is the new class of ultraportable PCs from the likes of PC stalwarts Lenovo and Hewlett-Packard and startups such as Oqo. Weighing in at four pounds or less, these devices are easy to carry around, and they offer displays that are far better than a two-inch screen.

The issue is not Web access, per se. Instead, it's access through the Internet to video and other multimedia content, which newer devices make such a simple and enjoyable experience.

Statistics from ComScore say that 9.1 billion videos were viewed online by July 2007. Last year, according to a New York Times article, video uploading and downloading from sites such as YouTube "consumed as much bandwidth as the entire Internet did in 2000." The trend is only expected to grow. In four years, according to MultiMedia Research Group, there will be 240 million video-enabled phones, as well as 63.6 million IPTV (Internet Protocol TV) subscribers by 2012.

Until recently, mobile Internet traffic has been mostly burst transmissions, such as e-mails, that can be more easily managed across the network without affecting the user experience. But video hogs the network for a good length of time, in the process squeezing out other traffic.

Most networks institute collision avoidance techniques so that various types of traffic don't get in each other's way, but that's harder to do with streaming media such as video. Typically, a local access point or cellular receiver will detect a video stream and make other traffic wait until the "gap" between video packets. Streaming media get priority because if there are too many gaps, the video or audio fragments. So other traffic such as Web pages and e-mails are forced to wait until the next available gap, likely leaving many users dissatisfied with the effective performance.