6GB of "other" on my iPhone 3GS, should I do a clean install of ios?
You can remove all settings and information from your iPhone using "Erase All Content and Settings" in Settings > General > Reset.

If that doesn't help you can also try the same from iTunes, see here for details.


Connect your iPhone to your computer
Select it when it appears under Devices
Select the Summary tab, and click the Restore button
verify to reset to factory settings and erase all data


Afterwards you can restore your data again from a previous backup in iTunes.