I use Nokia 7650 as a GPRS modem. First I create connection to my mobile through bluetooth as described in Affix Bluetooth HOWTO.

Then I get device /dev/btyx which I can use like a /dev/ttySx connected to modem.

Here we go to ppp connection to provider. Establishing PPP connection is described in GPRS PPP setting for Nokia mobiles (tested in Finnish Sonera & Radilinja networks) .