Yes, using a serial cable to connect to a cell phone and using that as a modem.
You didn't mention which Z or ROM, but here's how I did it on a C750 with Sharp ROM
1. In the Network app, setup an IRDA profile
2. Edit /etc/ppp/peers/IRDA?
add "/dev/ttyS0" as the first line to use the serial port
change baud to desired value
added "idle 500"
If you edit the profile with the network app, you'll need to make these changes again.
I think this is called the IRDA trick commonly used for setting up bluetooth connections.
wuurp