Unless they use the same size sim cards, all you need to do is swap sim cards. If they use different size sim cards, you will need to go to a corporate store and have them activate the proper sim for the proper line and phone.
This is a user to user forum. I am a user, just like almost everyone else on the site.
*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.