That was the case years ago. Right now major providers will not discount service price if you bring your own phone. They might give you a one time signup bonus

That was the case years ago. Right now major providers will not discount service price if you bring your own phone. They might give you a one time signup bonus when you join them. I.e. right now your option with the big three is to pay ~$50/month for the service with the fully paid off unlocked phone, or pay same ~$50/month with a free phone locked for 2-3 years.