Since Apple doesn’t allow third party apps in their iTunes store to run in the background, uploading your listened-to music in real time over the air (EDGE/3G/WiFi) is not possible. That is, unless you jailbreak your device and install MobileScrobbler. The free Last.FM iPhone app is for listening to online radio and checking listening histories, not for actual scrobbling.
Instead, you must install the Last.FM client on your PC with the iTunes plugin installed. The software will check the “Recently Played” playlist on your local machine to check the play count and last played fields to know when to upload new scrobbles. Now the whole issue I found was how it handles my iPod Touch. Basically, I am no longer able to manually handle my iPod’s playlist (which I’ve done since its purchase. Simply drag’n'drop to copy a single album in a flash.) You must set the device to be automatically synced with iTunes since it must copy the “Recently Played” entries to the local computer since the Last.FM client doesn’t pick up the connected iPod’s playlist. The sync process can take over 15 minutes just to upload what music you want to listen to. I have to restart iTunes after the sync until the Last.FM client picks up the scrobbles after an arbitrary few minute wait.
Also, if at any time you have an app crashes when using your iPod (say, Safari [every time you use it]), the play counts get reset and you lose any scrobbles from the last time you synced the iPod/iPhone.
