Denmark joins a growing number of countries where households and small businesses can buy converged Wi-Fi-cellular services.

Starting Friday, the Danish subsidiary of Sweden’s TeliaSonera will offer a service that allows users to make Wi-Fi calls at home and cell calls on the move, said TeliaSonera Denmark spokesman Rune Fick Hansen.

For 189 Danish kroner (US$32) per month, a household of up to five people can make unlimited calls to family members and all fixed networks in the country.

Samsung Electronics’ SCH-P200 will be the only dual-phone available at launch, but Telia Denmark is in talks with Motorola and Nokia to add more handsets, according to Hansen.

The Danish service, Home Free, is similar to the T-One service launched earlier this month by Germany’s Deutsche Telekom and the Fusion service rolled out last year by Britain’s BT Group.

Though usage is similar among all three services—customers use one phone that operates on two different networks—each offering has some technical differences, for good or bad.

Unlike T-One, which requires users to subscribe to Deutsche Telekom’s DSL service, Home Free allows customers to freely select their broadband service provider, whether cable, fixed line or wireless LAN.

"Cable is really big in Denmark, and we have many new companies providing Wi-Fi services in apartment buildings and other public areas," said Hansen. "No one is forced to purchase a broadband connection from a sole provider."

Like T-One, which requires customers to buy their cell phone service from Deutsche Telekom’s mobile subsidiary, Home Free gives users only one cell phone option: TeliaSonera.

Another distinction: T-One and Home Free use different technologies to move calls between Wi-Fi and cellular networks.

The German offering is based on Session Initiation Protocol, while the Danish service uses unlicensed mobile access (UMA) technology.

UMA enables a "seamless" hand-over of voice and data connections between global system for mobile communications and Wi-Fi or other local wireless networks. Additional information about UMA is available here.

BT’s Fusion service, which initially launched using Bluetooth but has since added Wi-Fi to extend its range, also uses UMA to hand over calls between cellular and local wireless networks.

TeliaSonera Denmark and BT aren’t alone in their use of UMA. The U.S. mobile arm of Deutsche Telekom, T-Mobile USA, is conducting a UMA-based pilot in Seattle, Wash. Telecom Italia and Orange also have UMA plans of their own.

Numerous manufacturers are eager to break into the nascent market for converged Wi-Fi-cellular phones. Earlier this year, Nokia announced its first UMA-based phone, the 6136. The world’s largest mobile phone maker is conducting an UMA pilot with local infrastructure providers in Finland.