Factory unlock with verizon?

I just bought a used iPhone 4S and want to get it on tmobile. I do not have a verizon card or anything though. I understand that you need to be a customer for at least 60 days. So could I just use a friends SIM card to unlock it and give it back. Would this do anything to their SIM card and would my phone still be unlocked when I give it back?

An iPhone that works on Verizon is probably a CDMA only cell phone as Verizon is a CDMA carrier. That means that it doesn't have a SIM card like GSM carriers like T-Mobile use. Therefore it is not a factory unlocked phone and will not work on T-Mobile's network or any other network.
However, if it is a factory unlocked phone, sticking your friend's SIM card in shouldn't be a problem and the phone should still be unlocked. I don't understand what you are talking about in reference to the Verizon card or needing to be their customer.