WiFi is an operator's best friend for relieving data congestion on the cellular network, but it's becoming a more viable network for voice calls, as well, thanks to technology Taqua announced Thursday.

The IP communications vendor Taqua LLC is launching a voice over WiFi (VoWiFi) virtual mobile core that it says provides fully integrated cellular-to-WiFi voice and messaging services on mobile devices.

A number of new mobile virtual network operators like Republic Wireless and Scratch Wireless have built their business on offering WiFi connectivity-first services. The biggest hand up for some of these startups is the transition from WiFi to cellular (Scratch's calls just drop, for example) or the need to launch an app to make the VoIP call, rather than using the phone's native dialer. (See Is WiFi the New It Network? and Why WiFi-First Works for Wireless.)

Taqua takes care of both of those things, but it's not targeting its offering at these alternative network operators. Its wants to offer the platform to mainstream cellular operators looking to compete with OTT VoIP apps. John Hoadley, wireless CTO at Taqua, told us it's already deployed on a Tier 1 US operator. Though he wouldn't say which one, leaks last week suggest that Sprint Corp. (NYSE: S) will soon begin offering voice over WiFi. T-Mobile US Inc. has offered a similar service for the past three years. (See Sprint Jibes With OTT Comms.)

Here's how it works: On the backend, the software treats the WiFi call like a circuit-switched 3G call, so it's routed the same, but over the unlicensed spectrum. Taqua's platform chooses the strongest signal and defaults to that network. It also uses the phone's native dialer, contacts, call history, voicemail, and SMS platform, so it happens without the user intervening or knowing.

Hoadley said this allows the operators to apply policy, track users, and bill for the call as data, instead of counting it against a user's voice minutes. It also gives cable companies a complement to their WiFi strategies. For consumers, it's a better option for indoor locations with poor cellular coverage.

Taqua plans to embed it on Android handsets, but it's also available as an over-the-air download to support older phones.

"People use WiFi anyway," Hoadley said; some reports say it handles 70-80% of all data use. "Why not bring voice over it?"

Taqua has been around since 1998 and has its hands in a number of technologies, including small cell backhaul and voice over LTE (VoLTE), but Frederick Reynolds, vice president of marketing at Taqua, told us VoWiFi is the area that's getting the most traction right now. In fact, both he and Hoadley have concerns about the operators' aggressive timelines for small cells and VoLTE, but that's a subject for another time. VoWiFi is something they want right now, Reynolds said, and the Taqua men believe that, when VoLTE is mainstream, VoWiFi will be a nice complement to it. (See More Startups Target Small-Cell Backhaul and Taqua Takes Tatara for Femto Voice Push.)

"We create a bridge between the features in a switch and IMS world," Reynolds said. "We can translate everything coming over SS7 to look like IMS on one side and SIP on the other. It's a useful transition that will last a couple of decades."

— Sarah Reedy, Senior Editor, Light Reading