What is domestic unlocking? Will my phone need to be unlocked and will it affect my network settings?

Your old carrier will have to domestically unlock your phone before you can bring it to Boost Mobile.

A domestic SIM unlock allows you to insert the universal SIM card into your device and attempt to activate it on the Sprint network. Unlocking your device will not necessarily make it interoperable with the Sprint network. In other words, a device designed for one network is not compatible with another network merely by unlocking it. Additionally, unlocking a device may enable some functionality of the device but not all (e.g. an unlocked device may support voice services but data services may not work or may be limited when activated on the Sprint network). Visit a Boost Mobile store to check your device’s compatibility.