In a first for US mobile carriers, Sprint has opened up an initial set of REST services for developers to play with for free at their new developer sandbox. With these services (Sprint API profile), developers can now access location, simple presence, and send SMS messages to Sprint handsets without requiring any software installed to the device.
Telephony and voice APIs are one of the most active segments of the API and mashup world. For example, in the past week, two of the latest mashups in our directory use telephony APIs in innovative ways (the directory has 42 telephony-related APIs):
AOL has just launched a new telephony web service for developers: the Open Voice API. This API is intended to "provide third-party developers and VoIP device manufacturers with open standards protocols that will enable them to easily integrate the AIM Call Out service into softphones, as well as SIP-enabled hardware and cell phones with wi-fi connectivity."