While T-Mobile's UMA offering has been around for years, Cablevision may be trying something new: Cablevision's COO mentioned in the company's earnings call today that the firm is testing phones that will switch seamlessly between cellular and Wi-Fi networks. That sounds an awful lot like UMA (unlicensed mobile access), a standard used for roaming by T-Mobile in the US and several carriers around the world.

T-Mobile offers UMA because it lets them leverage other companies' broadband and its network of home and roaming Wi-Fi networks. T-Mobile operates relatively few hotspots now compared to when it was anchored by Starbucks, but the key to UMA is voice over Wi-Fi over a wired or wireless broadband connection at home.

Cablevision has an even easier time of it, because it provides its CT/NY/NJ Wi-Fi network only to users that subscribe to its home cable broadband service. So any phone it offers can carry voice over Wi-Fi at home over its cable network and outdoors over its Wi-Fi network. In the past, Cablevision has partnered with Sprint for wireless service. However, I'm unaware of any production UMA gear that would work on Sprint's network.

The notion of UMA is to reduce the cost to a carrier of subscribers while providing subscribers with more unrestricted minutes. T-Mobile's plans, for instance, offer unlimited domestic calling over Wi-Fi even for plans with modest numbers of cellular minutes. This keeps customers loyal and happy with a lower cost structure. Femtocells have the potential to offer similar advantages to T-Mobile's competitors, but none are being priced or marketed in that way yet.