Hi, Ddw1! The iPhone X Compatible Models are the A1865 and the non carrier specific (Open Market Model). Yes, you'll need to purchase a new SIM card when you Bring Your Own Phone from a non-Boost Mobile wireless provider. Your new Boost Mobile SIM card will allow you to use the Boost Mobile network. To get a Boost Mobile SIM card kit, buy online, visit a Boost Mobile store or contact your local Walmart, Best Buy, or Target for product availability. It will not be locked on Boost network. You can find all the details here https://activate.boostmobile.com/bring-your-phone?intnav=TopNavhones:BringYourPhone.