Firstly i have to say that Z6 sucks when connecting with Linux compared to Nokia 2300/Siemens C25( chinese model 661 and most of other mini-usb or bluetooth equipped mobilephones.

Here is my success story of how to use Z6 as a bluetooth modem for Linux laptop to connect to internet.
1. save a copy of modem log under winxp motorola phone tools, which can make you access internet correctly.
2. on the phone side, enable blooth discovery, then bind it as a serial device on you laptop:
hcitool scan
rfcomm bind 0 <dev-id> 1
rfcomm show 0

then modify wvdial.conf, here is mine(generated by wvdailconf for phones of other brand):
[Dialer hellomoto]
Init1 = AT
Init2 = AT+CPIN?
Init3 = ATE0
Init4 = AT+CGDCONT=1,"IP","cmnet"
Init5 = AT+CGQREQ=1,0,0,0,0,0
Init6 = AT+CGQMIN=1,0,0,0,0,0
Modem Type = USB Modem
; Phone = <Target Phone Number>
ISDN = 0
; Password = <Your Password>
; Username = <Your Login Name>
Phone = *99***1#
; Modem = /dev/ttyACM0
Modem = /dev/rfcomm0
Username = 'cmnet'
Password = 'cmnet'
Baud = 460800

now, connect it:
wvdial hellomoto

you will have about 10-30 seconds to wait for the pppd up, you will notice some wierd log which could be a clue to hack wvdial for Z6 and V8.
viva, you can google with gprs/edge network now!