Bandwidth is allocated by your carrier to certain apps. System apps will take priority over games or user-installed apps.
It depends on the phone and the carrier. Some sell unlocked phones, other sell locked phones but you can ask them to unlock it. Others are not locked per-se but may be blocked from being used on certain networks. (In the US, for example, prepaid Verizon phones cannot be used on Page Plus.)
I Really Love Tech And I Think You Are All WRONG. It's Neither! It's NOT An Input. And It's NOT An Output! IT'S A STORAGE DEVICE!