H.M.
There are lots of great organizations out there that take your phone and give it to say an older person with heart problems, abused women, etc.
I'm a techy geek and you most certainly can wipe your phone. You can wipe your computer too. Why you can usually retrieve things is because memory isn't wiped it's just reassigned as available for something to be written on it when you delete something. So it's not gone it just went back into your available memory. It stays there as it is till something is written over it again. Think of it as recycling I guess. Lots of programs will actually go and "put" something on that old memory and then it goes back into the available memory. Sure the CIA might be able to retrieve things but the average person couldn't get a thing off my stuff or anyone's who didn't simply hit the delete key. Anyways, I don't think the CIA is wanting your phone to steal your old pictures.
If you are scared then go to your cell phone companies store and ask them to wipe them for you. They can restore your phone to factory settings and reboot it. All will be lost.
But any company that gets your phone will do this anyways. They have to put the firmware and such on it so it's able to work on their networks anyways.
It's sad that so many people would rather throw this stuff away than give it away because they are just sure their info could be lifted. What was really that important on your phone in the first place? Did you store your cc numbers on there? Your soc number? There are a heck of alot easier ways to steal your identity than that anyways. I've donated all my cell phones and I've never had my identity stolen. I've also donated all my old computers and laptops..... and still no identity stolen.