Libelium has introduced their 3G/GPRS shield for Arduino (3G + GPS). It enables connectivity to high speed WCDMA and HSPA cellular networks, and includes GPS. [via]
The GPS module also makes it possible to perform geolocation services even in indoors as it can work in A-GPS and S-GPS modes, so the location given by the GPS through NMEA sentences is completed with the cell information provided by both the 3G module and external Internet Geoposition Servers which helps you to get the most accurate location in each case.
3G/GPRS shield for Arduino - [Link]