Sprint Nextel's ambitious Xohm WiMax vision will be based on a radical change in the way users pay for the service compared with cellular plans.

Users will sign up for wireless broadband for a day, a month, or a year without a contract tied to a specific device. Payment could be made via a credit card wirelessly.

The pricing approach, described in broad strokes by Sprint chief technology officer Barry West Wednesday at WiMax World in Chicago, will be designed on the principle of "affordable" broadband and "around the needs of the individual," he said in an interview. That approach breaks down the concept now seen with cellular plans, in which users typically buy a two-year contract in part to subsidize the cost of a single mobile device that a user is locked into using.

A Sprint spokesman explained that the proposed pricing will rely on subscriptions, but not contracts in the sense associated with typical cellular contracts. And the longer the subscription a customer buys, the cheaper the service will be, he said.

West said Sprint will announce pricing early next year, but also said it will probably be based on tiers of service. The cost of devices, such as laptop cards able to transmit mobile WiMax, will approximate the cost of a 3G broadband laptop card today, he said.

In response to a question from an audience member, West also said that Xohm will not be backed by what the industry calls service-level agreements, a kind of guarantee that a minimum bandwidth will be provided or the customer receives a refund. "We will give you a good experience, but not SLAs," West said.

Several Sprint executives have described Xohm WiMax speeds that are expected to be 2Mbps to 4Mbps, although the technology is capable of 10Mbps. At a demonstration onboard a moving tour boat on the Chicago River Tuesday night using Motorola gear, mobile WiMax shared across 12 laptops and cell phones was clocked at 2.5Mbps downward. West noted that the demonstration was across only one channel, and that Sprint will be able to offer many channels to handle users at a single antenna site, offering plenty of bandwidth for many users.

West, who calls himself a technology "pragmatist," said he does not envision any hidden technology bugaboos in the nationwide rollout of Xohm planned for next year. In the next three years, he has predicted 50 million devices, such as laptops and mobile phones, will be WiMax-certified. Getting the certification process for interoperability in order will be difficult, but he said that even if there are 100,000 different devices, it is conceivable all of them could be served from only 10 different chip sets. "That's not unmanageable," he said.

By contrast, West said Xohm's biggest challenge will be servicing the needs of 210 million Internet users in the United States alone, and meeting their demands for access, applications, and services.

In his keynote, West said some critics have already begun to question whether West's predictions for Xohm's growth are too ambitious. He said commercial rollouts are still on schedule for the second quarter of 2008, and work has begun on 10,000 base stations nationally, with 20,000 WiMax antennas. The initial rollout in Chicago and Baltimore/Washington in December is "pretty much on target," he added.

As for competition, West said he doesn't see Verizon Wireless or AT&T.