[Reaktor5]

IPhone: Archive Your Texts with iPhone Backup SMS Extractor

No jailbreaking required!
I have yet to try this out but it does look interesting.

[jamesus]

This method is not as complicated as jailbreaking your phone to pull SMS data into a spreadsheet, but since you're sending your data to a web site, it's not as private or secure.

Yikes...sounds promising, but I'll pass on it due to that statement.