How to Remove All Personal Data On My Iphone?

I want to sell my Apple iPhone 4s on ebay but i don't want to reset it because I want to keep an app on it to sell however i don't want to remove everything but i want to get rid of all my personal data eg. Phone numbers, passwords, accounts and ID's. All i want left is my iPhone with an app on it with none of my info. Also, if i get rid of/disable my game center account, will this remove my app. Please don't give stupid, meaningless answers, thanks!

Added (1). If i back it up on my laptop, then reset my iphone. Can i get back my app by downloading it back onto my phone? I don't want to loose flappy birds!

Added (2). Right, -.- the app has been deleted from the app store and is rare and no longer available. If you read what i wrote then it might make sense

Added (3).… If i deleted all data off my phone without resetting, would whoever bought it be able to get my personal info, of anything that was removed back?

http://support.apple.com/.../kb/ht5661
read this link, all the information you need.
hope it helps.

Throw that nasty mother ***ker into boiling lava. It's the only way I know to permanently dispose of personal data. This is just because you told me not to.

Why don't you reset it, and THEN get the app again? Isn't that much easier? If you paid for the app, the app will always be connected to your account, and the other person will not have full access to it either way. Why would you want to keep a specific app anyway?

I would wipe it completely by following these steps: http://www.justtext.com/messageboards/20140127081812.html

I wouldn't leave it as is, jmo.