Yes Marc that is correct just purchase a sim with service
Once you have purchased your sim with service turn off the phone put the sim in it's slot. Then power the phone back on you will get a message i forgot what the message is. I saw the message one time because i had just gotten my phone and had not yet activated the phone with boost yet. I believe it said if i am not mistaken ????mode or Global Roaming mode it may have been some other words.
It is quite simple though you shouldn't have any problems Good Luck.