de-authorizing iphone4 on itunes

i had 3 iphones authorized in itunes (2 iphones 4s and 1 iphone 4) i sold the iPhone 4 but the guy that bought it said the apps i downloaded yesterday installed on his phone ..?..

You have to deauthorize the phone from your account - unfortunately this has to be done on the phone. If the guy you sold it to won't do this (or you want to make sure), click on "iTunes Store" in your iTunes, then on your Apple ID in the upper right corner. Enter your password. After that you'll see a page with personal information. Under "Apple ID summary" click "Deauthorize all". This will deauthorize all devices from your account. It's then pretty easy to authorize your devices again (e.g. in iTunes in the menu bar under "Store" -> Authorize this Computer).

That should fix it for you!

How do you do it on the iPhone

You are welcome!

You can't - typing "deauthorize iPhone" you'll see that i-devices cannot be deauthorized. You have to do that through iTunes on your computer.

I de-authorized computer ,,, plugged in my iPhone and re-set it up ,, downloaded an app ,, my buddy phoned and told me it also loaded on my old phone ,,,

Please read dekan's post #2 again. He said to go into your iTunes account on iTunes on your computer and deauthorize ALL DEVICES. Did you do that? I ask because that's not what you said you did in your follow up.

ok ya i got it now .. thank you for the help .. i got it de-authorized using the old phone , good thing i sold it fairly local ..