That means you eventually could walk down the street talking over a cellular network, and the call will seamlessly switch to voice over WLAN when you enter your office, which would cut down on the number of cellular minutes you and your company must purchase. Another example: Software in your phone will automatically route your calls over a voice-over-WLAN system when you are inside a warehouse where the cellular signal is weak and switch to the cellular network when you are outside where the WLAN doesn't reach.

Most important, perhaps, is the possibility that this emerging trend -- and the convergence technology behind it -- could create new challengers to cellular and landline operators. That, in turn, could lead to new and more intense competition.

"Cellular operators aren't thrilled about this idea yet," said Derek Kerton, principal of Kerton Group, a telephone market research and consulting firm. "If [subscribers] think they could cut their [cellular] service from, say, 1,000 minutes to 200 minutes, that explains why they're not too excited."

"Everything is starting to blend, and there are no clear lines about who will provide what kind of service," acknowledged Tony Krueck, vice president of product development for Sprint. "It'll take a while to work itself out."

The technologies