iPhone IMEI Unlock Then Keep Using Orig Carrier OK?

Hello everyone, I have a question regarding IMEI unlocks for Iphones.

I have a 4s still under contract w/ AT&T and heard that it is generally possible to get one unlocked thru an IMEI Unlock.

Here are some questions I have concerning the IMEI unlock process:
1. Will it be possible to have my iphone unlocked while it is still under contract?

2. Once I get it unlocked, am I required to use diff carrier's sim card or can I keep using my original AT&T sim for the time being until I find a new phone or carrier? In other words, will AT&T find out about this unauthorised unlock and relock my iphone if I continue using the same sim card? (I understand the logic of using same carrier after unlock does not make sense, but bear with me)

3. My ultimate goal is to get the latest iphone (factory unlocked from Apple) under my account and send this current 4s to my relative if I can get it to unlock. Once I get it unlocked should I then report as lost and then send it? Would this restore the lock since I have now essentially blacklisted it? Or should I first report it lost and then get an EMEI unlock?

P.S. Not sure if this makes any difference, but I am planning on sending this 4s overseas.

Thank you everyone. I really appreciate the help

thanks

Thanks for the reply, PsstGreek.

I figured I would report it as stolen/lost so as to remove that phone from my account, and then substitute-in the new iphone. Don't I need to give a reason to detach a phone from my account considering AT&T subsidized its cost?