If a serial converter uses the Prolific PL2303 chip, I'd put money on it working with the 2.6 kernel used by the 770.

I'm also working on getting a Bluetooth > Serial module working...I work for a company that sells them. More for experimenters though, it's a pin header device with 3.3V logic and costs about $60. Anyway I've gotten it to show up in "hcitool scan" and played with some pairing and rfcomm binding, but not quite there yet.

A cable that started in a mini-USB plug and ended with a 9-pin RS232 port would be useful, especially if it had a molded in compartment to hold some AAAs. Wonder how long a couple of lithium coin cells would power a converter like that....many RS232 converters have an openable shell and possibly enough extra space for some coin cells. Actually the one sitting on my desk does...and it has a USB B plug. Now all I need is a mini-USB to B cable.