So I fixed push on my phone with an unactivated AT&T sim card then I used the same sim card to fix my cousins Push too...Question is will it mess up since we both used the same AT&T sim card to fix it?
No it doesn't require anything special, it just reads the ATT sim card to act like it's activating...it isn't sending anything to anyone nor adding anything on the phone. Should work just fine using the same sim card on any iPhone