SMS Backup+ is basically what it says in the name, it is a Free application for backing up all of your SMS messages to your GMail account.
How does it do this ? well it is very simple, it converts all of your SMS’s messages into an e-mail like thread and then sends up a copy to your GMail account in a sub folder called SMS.
When it comes to restoring all it does it pull the same messages down fro the SMS folder and places them back into your Messages application (in order)
Here is a quick video review of SMS Backup+