GPRS

GPRS Modem is basically a GSM cell phone on a PCMCIA card, with a little antenna sticking out.

It will let you connect to an always-on General Packet Radio Service network.

In ye olden times, you would connect using a modem on a regular phone line (POTS) to a modem on the other end, establish a PPP link... and communicate.

GPRS allows you to connect/communicate directly with packets, i.e. you don't need a modem anymore — since it's all digital to begin with (modem, being a MODulator DEModulator, i.e. converter between analog and digital).
So, not needing a modem is good thing... but far more interesting is the fact, that since it's packet radio service, you don't need to dial either. Dialing took a lot of time, and you actually had to have a phone number to dial.

With packet radio service, you only need a profile and send the packets away.

Here is the critical part of my pppd(8) invocation, to get a ppp link across a GPRS modem:

• AT+cfun=1 Turns the GPRS modem on
• AT+cgreg=1 Starts the registration process (onto the GSM network)
• AT+cgdcont=2,"IP","proxy" Defines the profile to be IP connection
• ATD*99***2# Connects/activates the profile #2 (IP connection)

And pppd(8) takes care of the rest... authenticating and initiating the ppp connection.