Song plays not registering on iPhone 4

Take it off of manually manage music. That's what's causing the issue.

Years ago, it was a well-known fact that setting caused play counts to not transfer back to iTunes. It sounds like that is still the case.

Make a "Recently Played" smart playlist directly on the iPhone (while connected to iTunes of course), use "Last Played Is In The Last 14 Days" as the criteria. If it populates as it should, then you can Scrobble to Last.fm ... if I recall, if you manually manage the process is slightly different. Maybe check on the Last.fm forum for Scrobbling.

Just re-read your post ... are you certain that the playcounts on the iPhone are not updating? If so, are you playing music from the native iOS Music app on the iPhone, or a 3rd party player (e.g. Bongiovi, Album Mixer, etc.)? If you're using something other than than the native Music app player for the songs on your iPhone, some of those won't update play history.

Also, there Last.fm released an updated Scrobbler app that will let you play music that is on your iPhone or iPad, and do live scrobbling (as long as you have an internet connection). I played around with it yesterday and it will update play history on the device, as well as live scrobble.

The problem is that, to my knowledge, you cannot avoid turning off manually manage music if you want play counts tracked.

You can either let iTunes manage your syncing and keep track of play counts, or you can manually manage your music and not keep track of play counts. It's been that way ever since I've been using iTunes (1995).

A couple clarifications ...

Greg you're right about manually managing an iPod, under manual management any play history or rating changes from the iPod don't update your library. However, there was a time when the iPhone behaved differently such that plays and rating changes would register with iTunes even if you were manually managing. There is a thread somewhere around here on how this changed such that the iPhone behaves like the iPods do (either an iOS or iTunes update about a year ago changed this).

In any case, even under manual management the playcounts on the device itself should increment, that's always been the case for iPods and all other devices. If this is not happening, then perhaps an iOS and/or iTunes update changed that behavior. I refuse to manually manage, so I don't know if this is a bug or if the OP's device needs to be Reset or Restored to correct this.