How to securely erase an iPhone?

Hi,

I have an old iPhone 4 that I want to sell but I first want to make sure that the data is securely erased. I know how to wipe out the phone using Settings -> General -> Reset -> Erase All Content and Settings but have been told that if someone really wanted to, they could still recover data from an iPhone that was "wiped" in this manner. At the risk of sounding paranoid, I'd like to make sure it's securely erased (like writing zeros to a hard drive).

iClarified has a detailed explanation of how to securely erase an iPhone but it involves jailbreaking the phone first. Sort of ironic that I have to learn to jailbreak my phone just so I can wipe it clean and sell it (where it will be back to being un-jailbroken).

http://www.iclarified.com/entry/index.php?enid=1347

I've made it through step 4 (phone is jailbroken) but can't figure out how to get through step 5 which basically involves installing the BSD Subsystem or SSH, both of which need Installer on the jailbroken phone. Does anybody have a clue how to get BSD Subsystem or SSH on my iPhone 4? Better yet, anyone have a better way to securely erase everything on my iPhone?

Thanks,

Steve