T-Mobile GPRS via Prolific PL2303 cable in Sarge

[Carl Fink <carlf@fink.to>]

I'm using Debian Sarge on my laptop, and I'd like to be able to
connect that laptop to the Internet via my T-Mobile GPRS account,
using my Nokia 6800 phone and a connection cable that claims to be a
Nokia DKU-5.

When I plug the cable into the phone, it's detected as a "Data
Accessory".  When I plug it into the computer, it's detected as
follows:

    Feb 27 00:29:56 localhost kernel: ohci_hcd 0000:00:01.2: remote wakeup
    Feb 27 00:29:57 localhost kernel: usb 1-3: new full speed USB device using address 2
    Feb 27 00:29:58 localhost kernel: drivers/usb/serial/usb-serial.c: USB Serial support registered for Generic
    Feb 27 00:29:58 localhost kernel: usbcore: registered new driver usbserial
    Feb 27 00:29:58 localhost kernel: drivers/usb/serial/usb-serial.c: USB Serial Driver core v2.0
    Feb 27 00:29:58 localhost usb.agent[3179]:      pl2303: loaded successfully
    Feb 27 00:29:58 localhost kernel: drivers/usb/serial/usb-serial.c: USB Serial support registered for PL-2303
    Feb 27 00:29:58 localhost kernel: pl2303 1-3:1.0: PL-2303 converter detected
    Feb 27 00:29:58 localhost kernel: usb 1-3: PL-2303 converter now attached to ttyUSB0 (or usb/tts/0 for devfs)
    Feb 27 00:29:58 localhost kernel: usbcore: registered new driver pl2303
    Feb 27 00:29:58 localhost kernel: drivers/usb/serial/pl2303.c: Prolific PL2303 USB to serial adaptor driver v0.10

So far so good.  However, when I copied the chatscripts and peer file
from this page
(http://www.linuxdevcenter.com/pub/a/linux/2004/02/05/linux_cellular.html),
I was not able to connect.  I replaced his /dev/ttyS2 with
/dev/ttyUSB0 (per the message above from /var/log/messages). 
However, the modem never responds to the ATZ with OK, so the script
stalls.  I tried Minicom, and there also there's no reaction to ATZ.

I looked at some other postings by people who've used T-Mobile with
this cable, and some of them use the devfs version of the script,
such as "/dev/usb/acm/0".  I don't have an "acm" directory under
/dev/usb, so I tried "/dev/usb/tts/0" (per the messages from cable
detection) but pppd doesn't recognize that as a valid device and
doesn't even attempt a connection.  Turns out that this directory
also doesn't exist.

The phone/cable combo works fine under Windows XP (if I remove the
BlueTooth drivers, oddly enough).

Any suggestions about how to further investigate or proceed?  Thanks.
-- 
Carl Fink                  carl@fink.to
Ask me about I-Con 24, April 8-10, 2005
http://iconsf.org