s it enough bandwidth to stream audio from shoutcast?

Probably not reliably, or reliably enough for it to sound good.

If not, maybe it could send map data for gps?
Which I can't use while I'm eating its serial port

You could have a simple read-only imap email client running.
I could just do it on the treo.

You could probably use GPS and this to send your coordinates to a web server somewhere, and retrieve a map periodically for display.
I considered this, see above though. Also, realize for me, I'd just use APRS, but if you don't have an amateur radio license this doesn't help.