I have exacly the same problem with my BB 8310 (GSM, E-Plus Germany) and Ubuntu 7.10. I'm on it for a week now without any success. I'm in contact with a developer of the XmBlackBerry project, as they provided a fix for a bug in the Blackberry modems, but this is currently not working...
The problem is not in the (your) chatscript or the peer option file, but the blackberry itself, as all is working perfectly with a RAZR without changing an option.
You can go here: SourceForge.net Repository - [xmblackberry] Index of /XmBlackBerry/gprs_protocol_fix
Grab the gprs_protocol_fix.c and compile it with "gcc -o gprs_protocol_fix gprs_protocol_fix.c" and use
pty "<path to program>/gprs_protocol_fix /dev/rfcomm0" instead of /dev/rfcomm0 in you ppp peer option file. Maybe it works for you, for me it doesn't.
Maybe it's a bug in the Ubuntu 7.10's pppd or the latest device firmware for my BB. Will test it with another distribution.
PS: Using USB for modem access sometimes crashed by BB, but else it doesn't matter, Bluetooth and USB the same problems.
PS2: I tried it with Win, and USB and Bluetooth worked without any problems. So the Windows Dialer kann better handle the uniques of the BB modem... Would be interessting so see what exacly on Windows happens while dialing, but there is no console output or log file like in linux, or am i wrong?