Sprint has addressed indoor mobile network coverage issues by enabling its customers to make voice calls and send text messages over their home WiFi networks, the company providing the software behind the service announced on Tuesday.

The U.S. mobile operator launched Kineto Wireless' Smart WiFi client to facilitate WiFi calling on Friday, Ken Kolderup, Kineto's chief marketing officer, told Total Telecom on the sidelines of Mobile World Congress. It will come preloaded on Android handsets.

10%-25% of mobile subscribers have poor indoor coverage and "that's a big problem," said Kolderup. But many of those have WiFi at home and are already connecting their smartphones to it as a matter of course, he said. Sprint is taking that a step further and allowing them to use voice and SMS over WiFi too.

While telcos are starting to focus more on the data side of the business, "for many [voice] is still a huge percentage of their revenues," and they are investing to make the experience better for customers, Kolderup said.

That said, operators are always looking to reduce their costs, and Kineto's solution comes in cheaper than some alternatives because it leverages the installed base of home WiFi routers.

It could cost an operator in the region of $100-$200 to provide a customer with a femtocell, which means it is "very difficult to make that a mass-market proposition," Kolderup said. By contrast, Kineto's solution sees the operator spend "a couple of dollars on some software," he added.

"[Smart WiFi] turns every WiFi hotspot in the world into a femtocell," he went on. "[Operators get] the benefits of a femtocell at a fraction of the cost."

Kineto anticipates selling Smart WiFi elsewhere in the world, since "coverage is a pretty universal problem", although the fact that it requires IMS infrastructure means it will largely be restricted to developed markets.

The firm has yet to broker any operator deals in Europe, but "we have plans," Kolderup said.