How to download iOS 5 and backup?

I've got an old model unlocked/jailbroken of iPhone 3G. I wanted to update for the iOS 5.before updating I need to backup all datas, my contacts and SMS WITHOUT iTunes.

3G the latest iOS can install is 4.2.1
you can't update to iOS5
instead you can update to iOS4.4.2.1
but you will need iTunes.without it you can't do nothing.
download itunes from apple.com
install it, connect your 3g to itunes, make a backup, right click on backup now.
then let it update via itunes.
you can jailbreak again by guidance in some websites like: www.redmondpie.com