IDG offers more details on T-Mobile, British Telecom joining Worldwide Broadband Alliance: When I spoke to Sprint PCS about their Wi-Fi plans two days ago, they repeatedly noted that T-Mobile's closed network didn't help T-Mobile that much because the company lacks tier one locations. Sprint PCS's avowed plan is to allow roaming on their network and partner to allow their customers roaming on other networks.
While today's word that T-Mobile and British Telecom will join a mostly Asian roaming alliance seems to be a chink in that wall, don't forget Pass One, which comprises Wayport, FatPort, and three networks you've probably never heard of. This consortium was something Wayport trumpeted briefly as a way to increase international traffic before they moved on to opening their network for access for a fee to all the aggregators and resellers.
The difference between Pass One and the Worldwide Broadband Alliance is that the former has hundreds of locations, and the latter at least 10,000 already, with 20,000 predicted. Fold in T-Mobile and British Telecom's 2003 footprint expectations, and that's practically another 4,000 to 5,000 of the total.
But it's hard to say whether this "openness" bodes well for roaming intra-U.S., and whether it's of the old-school cell roaming pricing, like a buck a minute for using someone else's network. The key advantage of this alliance should be single log-on, single bill. But if you wind up paying more for roaming than for buying pay-as-you-go time, the roaming alliance would make no sense.