How can I tell if an Android device is locked to a specific carrier?

I want to know if an Android tablet is specific to a cellular carrier (T-Mobile, Verizon, etc.). The particular one I have in my hand now is a Samsung Galaxy Tab A, but I have multiple types of tablets in my environment, so I need to know a way to understand if the tablet is locked to T-Mobile or if I can simply swap SIMs to a different carrier. Where can I look in my T-Mobile tablet to check?