iPhone 2G, still under warranty, But Unlocked, what of warranty?

[175170]

I have a 2G iPhone that I took to the Apple Store yesterday.
The phone is currently on T-Mobile, but before taking the phone into the store, I removed the SIM card, so it seemed like it was a regular iPhone. There is no Cydia/ Installer, or any traces of hacking on this phone.
I also know for a fact that Apple cannot tell whether a phone is unlocked or not, as long as they don't have a different SIM card to test it with.
So anyways, the Genius determined that my phone's battery was under 1/2, and took out the SIM card and was ready to give me a new one. However, then he took the SIM card and put it into the new phone. Upon doing that, he plugged the phone in and was about to activate it for me.
I told him that I was capable of activating the phone at home , but according to him, he couldn't let me leave the store with an unactivated iPhone.
The only choice I have now seems to be getting a GoPhone SIM and going into the Apple Store and trying to get them to replace it again.
Any thoughts about this?
Thanks!

 

[tmac13]

They won't do it.

 

[benflick]

Yesterday, I got my 3G replaced, and since it's unlocked, I restored it before bringing it in.
Upon opening the new iPhone, the genius told me to put an AT&T prepaid sim in it to activate it. I was allowed to leave the store without the iPhone being activated...