retrieving deleted messages

By restoring to a backup made while they were still on your phone. You will have to restore the entire backup, not just messages.

The only way to do this and not use 3rd party apps is to restore from a previous backup. Restoring from the most recent backup will bring the text messages back to date of the backup, not any past that date though.

If that won't work, then using a 3rd party application is your only bet.

I hope this helps.

Right. There's actually no way to restore from backup other than the entire thing. You can't choose WHAT to restore from the backup... it's all or nothing.

Assuming it's a backup on your computer made with itunes, this article will show you what is backed up: http://support.apple.com/kb/HT4946. (See "iTunes will back up the following information".)