How to back up my iphone but not back up my messages?

Every time I try to delete my messages on my iPhone 4s, even if it's just a few, all my messages will be erased. Then the messaging app won't work until I turn it off and back on but then all my messages are back! I need to delete my messages somehow and the guy at the Apple store said the only way to delete my messages now is to restore my phone. I do not want to lose my contacts, as I have very many, and I also don't want to lose my apps and/or my pictures. Does anybody know how to get rid of these messages but still allow me to have my contacts and pictures and apps?

Added (1). I'm not stupid, please do not tell me to just swipe and delete my messages. I'm aware how one would normally delete a message but if you actually read the additional details I explain that that just simply is not working.

Just swipe and delete the entire message for each name.

Www.joule-phon.blogspot.com

checkout second link on