Thanks for the info. I now got GPRS working, too. I still needed to figure out the number to dial (*99***1# appears to work for most recent Siemens mobiles) and the additional modem initialization string (something like AT+cgdcont=1,"IP","<APN>", where <APN> denotes the GPRS access point, "internet.t-mobile" for my provider). BTW, the data needed for some German providers can be found on http://www.teltarif.de/i/gprs-config.html
Hmm, GPRS seems to be fairly expensive over here. I have to pay €0,09 for each 10KB.
Does anyone know a cheaper provider (flat rate maybe?) in Germany?
To avoid GPRS, I also tried CSD, but couldn't get it to work so far, at least not with my regular ISP (T-Online). The connection would build up ok, go past authentication, and then after about 60 secs the mobile would just terminate the connection. Has anyone else seen this, and maybe found a solution?
Anyway, thanks a lot again for your help.