Voice-over-Wi-Fi service is heating up in the enterprise. Research In Motion this week announced a new version of its Mobile Voice System (MVS) that now supports voice-over-Wi-Fi calling. MVS is installed in businesses and enables workers to use their regular desk phone number and extension from their BlackBerry smartphones.

By adding voice over Wi-Fi, business users can make and receive office phone calls via their BlackBerry devices over a Wi-Fi connection, saving on long-distance, international-roaming and even mobile wireless charges, said Manish Punjabi, senior director of collaboration, mobile voice with RIM. Punjabi said the solution is ideal for employees that are frequently away from their offices in construction, healthcare and sales industries, to name a few.

MVS 5 also includes some advanced IT features, such as Wi-Fi network access controls, that can set parameters in terms of what Wi-Fi networks employees are allowed to access, network-preference settings that allow enterprises to prioritize the use of Wi-Fi over cellular when it comes to voice calls and authentication to make sure that only authorized BlackBerry devices have access to the corporate network.

MVS 5 includes a smartphone client software application that enterprises can distribute over the air to BlackBerry users through the corporate BlackBerry Enterprise Server (BES) and BlackBerry MVS Server that connects the BES and the corporate PBX system.

In addition, the session initiation protocol (SIP) has been added to the MVS 5 to enable any SIP-compliant PBX system to connect to the MVS system. Punjabi said that previous versions of the MVS have only been compatible with the Cisco Unified Communications Manager. MVS 5 is expected to be available later this year.

In other news, T-Mobile USA announced it logs an average of 1.6 million Wi-Fi calls per month. In October, the operator launched a service called Wi-Fi Calling with MobileOffice that enables users with T-Mobile BlackBerry devices to use Wi-Fi and have the same number as their desk phones.

The service also connects into a PBX system, but T-Mobile's service requires a UMA (universal mobile access) client built into the device. To address this, T-Mobile this week introduced a new T-Mobile Solution Providers program — a cooperative effort between T-Mobile and WLAN resellers/system integrators to ensure that customers are both optimized for UMA and have voice-optimized Wi-Fi networks.