The culprit was indeed a b0rked USB cable. :D
I was also confused as to what IP I should assign to the usb0 interface.
The gp2x is using 192.168.0.2, which is what I was originally assigning to usb0.
I changed the IP for usb0 to 192.168.0.1 and was then able to telnet to the gp2x.
Thanks for...