It is the performance of the Xohm network so far that has people excited. According to Shen, subscribers are experiencing download speeds of 2 to 4 Mbps on average, with bursts to 10 Mbps, and upload speeds of 500 Kbps to 1 Mbps. Independent testers corroborate this.

More importantly, they're experiencing that kind of network throughput in moving vehicles. It may not be 4G speeds by the ITU definition, but it's fast enough to view flawless near-broadcast quality streaming video in a moving vehicle, as Xohm and independent testers have demonstrated.

A couple of interesting features of the fledgling service give hope for the 4G future, even if WiMAX 16e can't offer the 100-Mbps speeds expected with true 4G technologies.

One is that subscribers have an option to pay $50 a month for access - apparently unlimited: the Xohm Web site mentions no download caps - both at home (with the purchase of an $80 modem) and on the go. And that fee is guaranteed not to go up as long as they keep the service.

Will this set the pricing bar for data-over-4G? If so, the future looks bright indeed.

Such low pricing is possible in part because of the spectral and other efficiencies of WiMAX 16e networks. And those efficiencies should carry through to true 4G networks, which are expected to use a lot of the same technology as today's WiMAX.

Still, it sounds too good to be true—which means it probably is.

Another hopeful sign is that the network is "open" in a sense that traditional mobile networks, at least in North America, are not. Anyone can access the Xohm network at any time as long as they have a compatible WiMAX device.

Yes, Xohm is pushing monthly contracts but, like Wi-Fi hotspot operators, it will also provide access for a day (for as little as $5).

The network is open as well in the sense that there are no unreasonable restrictions on how you can use it - including to make VoIP calls.

"Any Internet application should be able to work on this network," Shen says. "Voice over IP applications such as Skype are just one of the existing Internet applications out there today. So we're not going to shut them down or block them."

"We're really trying to create a data business and we want it to be open."

This raises some interesting questions about the business models that might prevail in a 4G world. Will other operators be forced to adopt the same open network approach as Sprint? Indeed, can Sprint continue indefinitely along this path without risking damage to its core business?

"I think the carriers should move to more open networks," says Zeus Kerravala, a senior vice president at Yankee Group. "Open-ness breeds innovation. It's good for everyone."

Maybe. But guaranteed not everyone will see it that way.

Because of its third-place position in the U.S. cellular market, Sprint has "nothing to lose and everything to gain" by opening up, Kerravala says. But front-runners AT&T and Verizon are much more likely to want to hang on to the tight control they have over their networks today.