If you want to be able to hear the ringtone and audio thru the headset then go and download Freedom
www.toysoft.ca/freedom.html
with the Treo the only buttons are active during sleep are the hardkeys and the power on/off switch.
I just downloaded the 10 day trial version and it works PERFECTLY. I can listen to my mp3's through the headset (in mono or stereo), I can plug in a regular headset, and best of all I can turn off the exterior speaker and pipe the ring tones through the headset. Also, when I'm listening to MP3's, and a phone call comes in, it stops the MP3 from playing, and plays the ring tone. I can then answer the phone with the headset button.
Awesome!
James