A quick clarification for @George and @jerry_nixon, the Win8 inbox Windows Location Provider will not use Cell tower information to provide location, so there is no inbox Cellular location provider to the Geolocation API.  That is, just having a SIM in a Win8 device will not automatically start providing location from cell towers.  But a developer could create a location sensor driver (no easy task: http://msdn.microsoft.com/en-us/library/windows/hardware/ff545919(v=vs.85).aspx ) that consumes cell data and exposes the location to the Geolocation API so that any app developer can easily use that location data via Geolocation API along with the location data from other sources already available (Wi-Fi, IP, GPS).

 

Windows Phone, however, does use cell tower based location by default as that is always available.  The Win8 and Win Phone 8 Geolocation APIs (WinRT) are aligned so app developers can easily share code across those platforms.