my iphone 4 gsm only displays "restore needed".

Try to respring to do this hold power button and the home button at the same time and wait for the Apple logo to show up then it should turn of and on and again show you the apple logo let go of the buttons and let it boot and see if this works if not you need to post wheather this issue occurred during jailbreaking or any other form of software ulteration because from past user experience this is a common jailbreaking issue I currently am not jailbroken nor do I condone the use of such harsh methods they use to access the root directory of ios devices. So please provide more information so our users can help you.

pierrebasson wrote:

itunes says device locked needs passcode. no way I can enter one because it doesn't boot up that far. tried rebooting? what else can i do?

You need to restore the phone as described here: http://support.apple.com/kb/HT1808