How can I retrieve Notes data iPhone 3G

Notes are suppose to be a part of your mail. So besides being inside of your back up (by the way did you check icloud back up), they can sometimes be found inside of your yahoo(for example sake) mail. You could go to yahoo.com(example again-use your own), login and click notes on the left.

Tried already. No luck.

If you aren't backing up to iCloud your phone should back up every time you sync.  If you had your notes on your phone before you synced and haven't synced again since you should be able to restore to this backup to recover your notes.  This will revert all data and settings on your phone to those contained in the backup, not just notes.  If you haven't synced again since losing your notes and aren't backing up to iCloud and want to restore everything from your last backup including notes, do the following: