The gleaming black shuttle van slams down into a pothole, jolts and shudders over construction-scarred streets in downtown Baltimore, slows for late morning traffic and speeds up again, rattling over cobblestones.

But inside a handful of WiMAX-equipped notebook computers remain linked to Sprint's Xohm ("zome") network, showing consistent, and unprecedented, broadband wireless download speeds ranging from 3.7M to 5Mbps on the downlink and 1.8M to 2.6Mbps on the uplink.

On a flat-panel screen mounted at the rear of the van, the movie "Men in Black" streams from the Hulu.com video site without a flicker or blur, even as the van cruises through multiple handoffs between some of the 182 (and counting) WiMAX towers now blanketing about 75% of the city.

As a demonstration of what WiMAX and Xohm, the first large-scale mobile WiMAX network in the United States, is delivering, the van ride is dramatic.

In a nearby townhouse, a laptop plugs via Ethernet cable into a XyXEL WiMAX router, coupled with a massive Samsung flat-panel screen showing Internet news sites and streaming video in the living room. In the kitchen overlooking part of Baltimore harbor, two other laptops show a side-by-side speed-test comparison of Sprint's 3G network and Xohm: 678Kbps down, 520kbps up for 3G; 4.2Mbps down, 1.3 Mbps up for WiMAX.

Xohm’s target

As dramatic as the van ride was, it's the combination of residential wireless Internet access and nomadic laptop-based computing that will likely be the initial attraction for Xohm, which executives billed as the first 4G network in the United States.

"Xohm targets both segments [nomadic and fixed residential], and that's a powerful differentiator for WiMAX, because you cannot do this in a scalable way with 3G," says Monica Paolini, president of Senza Fili Consulting, a wireless consultancy. "Xohm basically supports what subscribers perceive as two services, primary, fixed home broadband and nomadic/mobile access, within a single network and, for subscribers, a single contract."

That target was underscored during a press conference on Wednesday, which featured a variant of the traditional ribbon-cutting ceremony: Barry West, Xohm president and CTO, posed with a two-handed lopping shears to cut through a blue Ethernet cable, as camera's flashed. "How about a special one for Verizon?" he joked, to another round of camera flashes, and then snipped through the cable.