Selling my 3GS - How do I erase all my info?

[Machog]

Very dumb question, how to I make sure I have totally cleaned off all my personal information from my iPhone 3GS?

Also want to make sure I don't erase any info from iTunes when my new 4S arrives later this week-its already been shipped yeaha, can't wait.

Tx Machog

 

[RoofMonkey]

Restore the phone as new and do not sync it.

 

[acosmichippo]

alternatively, Settings->General->Reset->Erase all content and settings.