A search of the Apple Support Boards turned up a way of backing up and restoring your iPhone which seemed to work for many people who tried it. The problem is it doesn't work for everyone and it takes a LONG time because you have back up your phone, restore it to factory settings and then do a complete restore from backup. This method seems to get rid of corrupted files which can often make up several GB of "Other" storage on your iPhone.
I did this and found it did not work for me. So, I was off to find another method and came across a method that uses a product called DiskAid. The iPhone' file system is completely closed to you the user. Other than some really crude tools in the phone itself and the bar in iTunes, you don't know how much storage is being used for what. And, you certainly don't know what files are on the phone or how big they are.
Here are the steps I took:
Step 1: Back up your iPhone.
Before you go messing around withe the file system in your iPhone, make sure you have a current backup. Plug your phone into your computer, go to iTunes, click on the iPhone's icon in the left column (under Devices) and under the "Summary" tab back up your phone. This way, worst case, if you really screw something up you can at least restore your phone back to the way it was.
Step 2: Turn of sync music in iTunes
Now go to the Music tab and uncheck "Sync Music". This will delete all the music from your iPhone (synced from iTunes) on the next sync. Don't worry. You've already backed up your phone.
Step 2: Install DiskAid on your PC/Mac
DiskAid is a fantastic product that allows you to actually see the files installed in your iPhone. You can then add or delete files just like you do on your computer. I was able to do everything I needed to do with the free version which was really, really easy to use. No hacking and no jail breaking necessary Several fixes I saw required me to me to jail break my phone. I am NOT going to jailbreak my phone.
Make sure your iPhone is connected with the USB when you open up DiskAid. You'll see a file system structure of your iPhone. Be careful when messing around in here because I believe DiskAid shows all files, including ones needed to operate your iPhone. You'll want to go to the File System part then the folder that says Media.
Step 3: Go into iTunes Control folder and then the Music folder
In the Media folder, you'll see "iTunes_Control" and under "iTunes_Control" you'll "Music". In music you'll see several folders all starting with "f". I see a total of 50 every time I open this up. You'll delete all of of those folder. You can select the first one, hit and hold "shift" and select the last one. Then, delete them.
note: when I did this the first time it got rid of about 2 GB of the "Other" I had been seeing in iTunes. Additional steps were necessary to clean all of the other out. This step should work for most people.
Step 4: Open iTunes and sync your iPhone
With the “music sync” still turned off in iTunes, sync your iPhone. You should have been warned when you turned off music sync the the next sync would delete all the music from your phone. It will.
Step 5: Unplug iPhone and reboot it
After the sync has completed, unplug your iPhone. Now, hold the power button at the top and the Home button on the front of your phone until you get the option to shut down the phone. Completely power it down by sliding the switch that will appear. Now turn the phone back on using the power button on the top.
Step 6: Reconnect your iPhone to iTunes and recheck “sync music”
This will sync your music back onto your iPhone. Check "sync music" and just sync your phone again.Step 7: Additional Steps May Be Required
Reading through the blog where I found the tip on DiskAid, I got the feeling this one step works for most people. But, it didn't work for many others. For me, this got rid of a bunch of the "Other" taking up valuable space on my iPhone- about 2GB. But, I still had about 3 GB of other. I tried the procedure again this time unchecking the "movies" from the sync. To do that, I just did the same thing but instead of looking for the "music" tab under iTunes, I looked for "movies". That took off about another 1 GB. Then, I tried the same thing with Photos. That didn't actually do anything.
One cool thing about DiskAid is that if you right click on a file or a folder you can click on "Get Info" and see how big it is. I did this on all of the folders in the Media folder and realized the "Recordings" folder was 2 GB. I looked inside there and found dozens of Voice Memo recordings I had done. I had deleted these recordings from iTunes and iTunes told me it was deleting them from my iPhone. That turned out not to be true. I deleted them using DiskAid and my "Other" was now down from 5 GB to under 1 GB. The strange thing is some of these recordings continue to pop back onto my iPhone and I have no idea where they're coming from. But, now I know how to get rid of them.