Can cellular companies control the phone call quality and data speed/quality over the network BASED on your identity?

Not a conspiratorial/ or privacy question…but more of a ‘does (or can) price buy quality?

ATT controls the vast majority of GSM towers in the USA. Yet they sell access to Tmoble, Mint, Consumer Cellular, etc etc. Can ATT give higher proiority to their own customers than their ‘renters’? DO THEY?

Not ‘will I get a signal’ or ‘will my phone ring’… more ‘is the bandwidth the same, is the call quality the same, for all users of a given network?’

I know ATT can give priority to first responders in an emergency situation….is a version of this how they sell capacity for cheap?

Anyone KNOW?