How to get rid of 'other' in iPhone memory?

I keep receiving the same error popup message on my phone, telling me I don't have enough memory to take any more pictures or download anything. When I plug my iPhone into my computer and open iTunes, I notice I have about 2.5GB of 'other' in my memory. I checked the Apple iPhone forums, and their suggestions were no help. I've also tried restoring from backup, but I can't seem to get rid of it. Any suggestions?

I know most of my "other" is messages and emails. If you don't delete them often they can take up a lot of storage.