Log into irc.saurik.com/#iphone and find eric. He and I made the MobileScrobbler port to the 2.x OS (Scrobbled). I believe MS works in a similar vain as what you you want. It gets the session id and uses that to log into the server to submit track information to the Last.fm web client.
Last.fm – The Social Music Revolution
He might just have an easy time making your app. I'd offer my assistance, but I have too many projects in front of me to accept another.
