Which cellular provider offers a service where subscribers can use their cell phones to roam between cellular and Wi-Fi networks for calls?
T-Mobile made HotSpot @Home easy to use. Calls placed in cellular zones transfer over to Wi-Fi networks (such as T-Mobile HotSpots) about 20 seconds after walking into the hotspot and vice versa. There is no indication to either the caller or callee that the call has transferred from one network to the other. It is a seamless e3xperience. However, call quality is still a work in progress, as users have experienced both good and poor quality on both T-Mobile's GSM network as well as the hotspots.
Data calls, (Internet), still connect through T-Mobile's Edge network, not the Wi-Fi system.
Users in poor coverage areas can definitely make good use of this enhanced coverage service. The ability to make unlimited "free" calls when on the Wi-Fi network is certainly appealing. This service is very attractive for the home office subscriber who also happens to be located in a poor coverage area and makes many phone calls per month.