Microsoft has just been granted a patent covering ad-hoc wireless connections for portable devices.
While the patent title specifically refers to portable media players, the patent itself references "wireless devices" in general, while noting that the "invention" is "not limited to such devices".
Ad-hoc W-Fi networks are particularly useful to establish short-range connections to other wireless devices that are connected to the same access point and use the same SSID and channel number. Microsoft's patent was filed in November 2010 and was quite obviously targeted for use in its Zune media players, which were retired in early 2011. The patent claim could be easily extended to smartphones as well as tablets.
From the patent: "According to a first aspect of the invention, a method to operate a wireless device in an ad hoc network is provided. The method comprises: transmitting and receiving discovery information by the wireless device during a discovery window of a periodic discovery interval; and operating the wireless device in a power save mode during an inactive portion of the periodic discovery interval."
It may be difficult, however, it may be nearly impossible for Microsoft to enforce the patent due to the existence of prior art and the rather general description of wireless devices in the patent.