I don’t think I’ve ever had a credit check for tmobile, mint, or others. I’ve never given my SS number to a phone company other than perhaps a landline last century.
They can also get it through autopay records. Banks give that out to them when they SHOULD NOT. Why do Banks give that out to them? For debt collection legalities. Without it they cannot legally collect a debt.
And this is why it is absolutely stupid to use autopay of any kind...