Daisychaning mp3 players to Treos

[Clinkypawses]

Just got my Treo 600 and am in love with it. But being greedy, I'm already thinking of ways to achieve good mp3 capacity and hands-free phone capabilities in one headset even if it means carrying two devices.

Is there any solution on the horizon to somehow have either:

1. a "T" audio jack that feeds mp3 player output in stereo through or by the Treo 600 headset input such that the music could be coming from (say) my iPod with the phone cutting in upon receiving a call?

2. a USB/smartcard adapter that can view an mp3 player as a hard drive from which to select mp3s for playback via Pocket Tunes?

3. (least preferrable, but still better than nothing) a way to grab mp3 files off a laptop folder via USB to play in Pocket Tunes or similar app?

Basically, I'm looking at a way to have access to more than 512 measly mb of mp3's while still being able to handle phone calls and not drain the battery quite as fast (assuming the mp3s come from a player or external hd/usb link).

Is the technology simply not there yet? Or has anyone found some 'hack' solutions to get some of this capability?