I use this method to take all music off iphone4:
With iphone plugged into computer, itunes>tick ON, Sync only checked songs & video>go to "Music" tab> tick ON, Entire music library//In itunes Library(top left of itunes, Click on Music>Go over to songs, (In any song)>Hold Command & mouse click on a songs checked box (all songs should be unchecked now)>go back to iphones window> Sync Entire Library (check)...Bottom, click SYNC.
BTW...Go back to music library and tick song boxes checked the same (Comm.+Mouse click) when finished.
You can also swipe finger across songs on iphone to delete them manually also.
Hope this helps.
There is an easier way to delete songs from iPhone 3G and above.
1. Take a backup of your songs in iTunes
2. Delete all the songs from iTunes (iTunes -> Library -> Music -> Select all songs and delete)
3. Sync your iPhone (all songs iPhone will be deleted)
4. Start afresh by reloading your favorite songs in iTunes and iPhone
It worked for me. Hope it works for you too.
- Tap on “Settings” and tap on “General”
- Select “Usage” and tap on “Music”
- Tap the Minus symbol next to “All Music” then tap on “Delete” to remove all songs from the device