can an unlocked phone just swap sims from another carrier?

Actually this is a two part question.

1. I called sprint to see if i can get my phone unlocked so that I could test it on another carrier. At first they refused, then they said ok and gave me the MSL # for the phone. Is that all that is needed if i wanted to go to t-mobile or some other carrier and switch the phone to them? Can I unlock the phone myself if i have the MSL #?

2. if the phone were unlocked, and I had a sim card from another carrier, could i just swap sim cards and use the phone on the other carrier? Or does the phone have to be activated with the carrier first? I've got a friend with a note 4 from t-mobile and i was hoping i could just pop his sim card into my phone to test my phone out on t-mobiles network. I don't really want to sign up for service unless i know for sure the service is better.

Thanks