How to retrieve data accidently deleted from my iphone Apple 3G?

How can I retrieve data accidently deleted from my iphone Apple 3G?

If you ever made a backup on your computer, just plug it in, open iTunes and hit restore. That will install all of the data that was backedup on that day.

If not, there won't be much way to retrieve it without going painful process, but that will probably cracking iphone down and I really don't know how to do that.