Well, you know that you would need something like a Keyspan USB to Serial converter, which would also have drivers for the OS you are running.
The short story is that you would be better off with a Netbook. I used to use a 12" Mac Powerbook G4 with a Keyspan connected to a Cisco rollover cable. I now have a 10" Lenovo netbook Hackintosh that can do this.
I haven't found any Linux drivers that support the keyspan well. And the Belkin converters really suck, IMO.
if you're an enterprising developer type, you could always write one for Android, and then many systems and network admins would be happy with you!
Best of luck.