Sprint brings Wi-Fi calling feature to newer iPhones, but smooth handoffs are MIA

Sprint's (NYSE:S) Wi-Fi calling service is coming to Apple's (NASDAQ: AAPL) iPhone. The carrier said that starting today, Sprint customers with an iPhone 6, 6 Plus, 5s and 5c will get access to the feature via an over-the-air software update that will be distributed over the next week.

Sprint said that with the addition of the iPhones into Sprint's roster of Wi-Fi calling devices, Sprint now has more than 25 smartphone models and more than 15 million customers with the ability to use Wi-Fi calling. Sprint has around 56 million total customers.

"Wi-Fi Calling is like a major expansion of our network, allowing Sprint customers to get coverage anywhere they have Wi-Fi connectivity," David Owens, senior vice president of product development for Sprint, said in a statement. "Traditional wireless technology has some limitations in places like basements and high-rise office buildings. Wi-Fi expands our customer's connectivity in a big way. The addition of Wi-Fi Calling for iPhone customers is just one more example of how Sprint is getting better every day."

A key benefit for Sprint customers is that they can make calls on Wi-Fi networks if they don't have a cellular signal. Customers can turn on Wi-Fi calling as an option in their settings when they have downloaded the software update.

Sprint spokeswoman Michelle Leff Mermelstein told FierceWireless that Wi-Fi calling on Sprint phones accesses the device's native dialer. However, she noted that Wi-Fi-to-cellular handoff is "not smooth" and that if a customer initiates a call in a Wi-Fi coverage area and then leaves Wi-Fi coverage the call will likely drop.

Taqua and Kineto Wireless were the vendors for the launch of Sprint's Wi-Fi calling service in 2014. Kineto's Smart Wi-Fi client lets Sprint subscribers to use their voice and messaging services over existing home, office and public Wi-Fi networks. Taqua's virtual mobile core system enables a handset to select between Wi-Fi and cellular, using the strongest signal for voice calls as well as messaging. Taqua acquired Kineto last year.

Sprint's Wi-Fi calling supports calling from more than 200 countries and territories, but is not supported in certain countries, including Australia, China, Cuba, North Korea, India, Iran, Singapore, Sudan and Syria.

T-Mobile US (NYSE:TMUS) has seen strong adoption of its Wi-Fi calling feature. According to Grant Castle, T-Mobile's vice president of engineering services and QA, the operator now counts 7 million users of Wi-Fi calling. T-Mobile supported Wi-Fi calling on the iPhone 6 and 6 Plus when they launched last fall. T-Mobile also says its solution supports Wi-Fi-to-cellular handoffs.

Last fall T-Mobile made a big push for Wi-Fi calling by letting customers upgrade to a new Wi-Fi capable smartphone if they didn't already have one. In addition, the carrier began offering Simple Choice postpaid customers a free proprietary "Cellspot" Wi-Fi router for their home to enhance their in-home coverage.

Verizon Wireless (NYSE: VZ) plans to introduce Wi-Fi calling in the middle of this year. The carrier's VoLTE service is available nationwide but only on 16 devices.

Ralph de la Vega, CEO of AT&T's (NYSE: T) Mobile & Business Solutions Group, said last September that AT&T will launch Wi-Fi calling in 2015 but that the carrier will use it only as a complement to VoLTE or 3G-based calling. In December, AT&T announced that it had deployed VoLTE in parts of the District of Columbia, Georgia, Illinois, Indiana, Maryland, Michigan, Minnesota, Nevada, North Carolina, Ohio, Oregon, Pennsylvania, South Carolina, Texas, Utah, Virginia, Washington and Wisconsin.

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