If you have back up your text messages, you can restore from the backup.
To restore information from a backup, use one of the following methods after connecting your iOS device to the computer with which you normally sync:
1. Right-click (or Control-click) the device and choose Restore from Backup
2. If you have a new phone, you can connect to iTunes and it will prompt to restore from your backup Solution from Apple.com: http://support.apple.com/kb/ht1766
If you have no backup for your data on iPhone, iPhone data recovery software is your last shot! I used Tenorshare iTunes Data Recovery and it worked well. It's easy to use. Just a few clicks you can get all your data back. Here is a step by step guide for you: http://goo.gl/FpOvb
An iTunes back up does save the SMS messages as long as they were on the phone when the back up was made. You can even check the article http://support.apple.com/kb/ht4946 which clearlhy states SMS are saved in a back up. I personally aswel always have my SMS saved in my back ups I've restored from.
if you had an iTunes backup taken, try this: http://support.apple.com/kb/ht1766
it's always reccomended to take backups. itunes takes automatic backups if you ever plug it into your Mac/PC. have a look. you may have a backup, without you knowing.
it may work, i havent tried this method.
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Only as part of the overall iPhone backup. They can't be accessess separately; they would only be available if you restore you phone to the backup, including all the other data and settings contained in the backup. If you want to save your message conversations separately, you'll either have to take screenshots and email them to yourself, or use 3rd party software such as Touch Copy (pc or mac) or PhoneView mac).