Ordering iPhone 5 Online

[firelord901]

I'm looking to order an iPhone 5. But I want it unlocked. My brother is an AT&T customer, and already has an iPhone 5. If I order it online using his account and the "replace a phone on my account with an iPhone" option, it comes up as unsubsidized (which I want so it's unlocked.) The part that has me concerned about ordering it using this method is the "When will my current phone stop working" part. If I took out the SIM card that ships with it, restored the OS, and put in an unactivated SIM, will it still automatically try to activate it as a replacement phone to my brother's account? Or would the replacement service automation be tied to the SIM card that ships with the phone, and not the phone's IMEI. Apple's website says "If purchasing from the Apple Online Store, your AT&T service will be transferred when you turn on your new iPhone for the first time and follow the onscreen instructions to activate it." Any advice or experience ordering this way?