Comparisons are often made between femtocells and the dual-mode WiFi/cellular solution such as UMA. In both cases, a strong early reason for takeup has been to improve call quality in areas of poor coverage. The short range of both WiFi and femtocells (at best a couple of hundred metres) means that operators are also able to target zone-specific tariff plans.
Home-Zone based tariff schemes
There have been several successful home-zone based tariff schemes which operators have used. These aim to switch users from making calls on the fixed phone network to the mobile network by providing cheaper calls in those places where they would be most likely to do so - typically at home or at work. Sophisticated systems have been put in place to map the registered home location (a ZIP code or other postal code) to the serving cell towers in the area.
The trouble has been that the coverage area of some cell towers may include much of the local area, so that calls made and received when out and about are also the one used most of the time. There is also the issue that 2G and 3G coverage areas differ, and is another factor for potential errors in determining when in the home zone. Operators have therefore leaned on the side of generosity, losing revenue that they would otherwise capture.
Fixed Mobile Substitution already winning
The switch to greater mobile phone usage is already very succesful. Fixed Mobile Substitution is encouraged by bundled minutes, where callers view minutes used within their plans as "free" compared with per-call charges on their fixed line. Combine this with the convenience of the mobile phone address book and some people go out of their way to use their mobile in preference to the fixed phone.
Femtocells are location specific
Femtocells are very much a location specific capability for the operator. In addition to improving coverage and achieving higher data rates/better data performance, they can allow operators to withdraw the outdoor home-zone packages and replace them with femtocells. CDMA femtocells such as Samsung's Ubicell incorporate a GPS receiver to verify their exact location, and therefore what frequency they should operate at (if at all). This could be used to prevent them being moved elsewhere.
Dual Mode WiFi services, such as UMA, on the other hand are device specific. You need to have a special UMA capable handset which automatically seeks out WiFi coverage and uses it where possible. Service providers such as T-Mobile USA allow any WiFi hotspot to be used to access the service - even when abroad, at public locations where WiFi is available or in corporate offices which provide WiFi for public use.
Femtocells enable location specific services
Due to their location specific nature, femtocells can enable additional services within their coverage area (known as femtozones). Whilst there's nothing to stop WiFi dual-mode handsets doing the same, at the time of writing, we might expect to see more focus on these connected home schemes.