Snootlab, a pure open hardware player, has designed this nice 2G/3G+GPS shield for Raspberry Pi (compatible with A/B/B+ versions). The design of the shield is provided in open source.
The shield is based on Sierra Wireless AirPrime SL8082T module, and can be used either as a bit pipe modem (thru I/Os or USB link) or as a smart modem accepting Open AT applications.
This shield is autonomous and comes with its own power supply and antenna, and powers the Raspberry Pi (then, the Raspberry Pi power supply is not used).
This shield can be used as well as an Open AT SL8082T dev kit when plugged in USB to a PC using the Open AT Application Framework (Developer Studio).
Open AT application framework: