Native? Nothing's native right now but if you have a jailbroken phone you might want to look into fring. http://www.fring.com/.

By native I mean't "third party - not web app"
fring .978 (available from installer) apparently doesn't support the iPod touch.

Depends if you consider this existing:

http://code.google.com...

wow - amazing.
This is exactly what I've been looking for for the longest time.... I was so disappointed when I realized fring was so buggy on the iPod touch... but this is exactly what I need and nothing more.
This even keeps the wifi active if the sleep button is pressed... and will still receive messages....
I wonder how much that effects battery life....
incredibly cool app.
Thanks!