GPRS

GSM data transmission technology such as GPRS (General Packet Radio Services) is a technology used for wireless data services such as wireless internet or intranet and multimedia services.
This technology is being developed, and, of course, such as wireless technology in the other world, this technology will be growing very quickly. Such as GPRS roaming is a basic requirement to realize a global mobile internet to customers in the different GPRS operator GPRS network in the future. This applied to the GRX, which is an IP routing network centralized for interconnection between the GPRS network. GRX system based on GPRS roaming has been successfully conducted between Sonera Roaming System network with Nokia's.

commtechm2m.com says :

The General Packet Radio Service (GPRS) network is an "always on", private network for data. It uses the existing GSM network to transmit and receive TCP/IP based data to and from GPRS mobile devices. Private IP addresses are typically dynamically assigned within the network to mobile devices. However, Access Point Names (APN's) provide a gateway route to other networks such as the Internet, WAP services or private corporate networks. Firewalls typically reside at the APN to isolate the public and private networks. IP addresses allocated to mobile GPRS devices are therefore not addressable from outside the GPRS network (e.g. from the Internet) without specialised services or infrastructure.

GPRS tutorial - GPRS elements diagram