Securely erasing my old iPhone prior to selling it

[m021478]

I am currently using an iPhone 3Gs, and I would now like to sell my original iPhone (1st-Gen), but I can't follow the well-documented "Erase All Content & Settings" instructions because my old iPhone currently doesn't have a SIM card installed in it.

Because of this, I can't get the phone to show me the springboard/homescreen (let alone grant me access to any of the settings to securely wipe it)... that is, unless I take my current SIM card out of my iPhone 3Gs and and put it back into my old phone - then, I would be able to go through the activation process with AT&T again from my old iPhone (1st-Gen)...

Doing this is the only way I can get the phone backup up and running to be able to securely wipe it using the "Preferences > General > Reset > Erase All Content & Settings" feature.

I was hoping someone might be able to tell me whether or not I would screw anything up permanently (like my Terms of Service/Contract with AT&T, or something along these lines) if I were to re-insert the SIM card back into my old iPhone; temporarily re-activate it so that I can wipe it; then reinsert the SIM card back into my iPhone 3Gs where it will remain.

Any suggestions would be greatly appreciated... Thanks!

 

[dragonmantek]

no, you won't get charged for anything. you still have the unlimited data plan, so anything you do won't have a negative effect on your bill.

if it helps, you already should have a back-up in your itunes of your old iphone, it stores it automatically i think, you can check iTunes --> Preferences --> Devices