It could also be unintentionally full flash memory. I have an iPhone 4 that was unbearably slow, and eventually started claiming there was not enough room to s

It could also be unintentionally full flash memory. I have an iPhone 4 that was unbearably slow, and eventually started claiming there was not enough room to sync music, despite supposedly having 2 - 3GB spare. (The 'other' section had somehow grown to 8GB, and after attempting a factory reset & resync, Other grew to 16GB instead of disappearing.) I fixed it by deleted all the music, syncing, and then manually selecting the music I wanted again. That got me back my free space and cleared the 'other' space. The device is now remarkably zippy again. [Obviously I have other phones, but I still use the iPhone 4 as an iPod & podcast device.]