Re: How can I 'wipe' my iPhone 3GS?
Tap Settings > General > Reset > Erase all Content and Settings. Now, I realize you said you did that and it stalled for a while but in some cases, that's actually quite normal so be sure to plug it in and have it charging while it goes through the process. If, for whatever reason, that fails.. You can connect to iTunes and restore the device as a new setup and just be sure to not load any back-ups you may have back onto it. Personally, the first option is the most secure but you can always run through it again after setting up the device as a new one IF you want to be REALLY sure the data is gone. You never mentioned it but just in case, if you have some jailbreaks installed that may also be preventing it from wiping normally. In that circumstance, you'd have to either remove all the jailbreaks or use the second method I mentioned. Reading through the comment section might also address any further concerns you may have - http://www.imore.com/tip-clear-erase-user-data-iphone
Originally Posted by iMore Question