I wouldn’t be surprised if they rip people off on cheaper phones, but for higher end phones the “free” phones are typically exactly the normal price of the phone split over 24 payments. Every time I buy a new phone I compare buying it directly versus via a carrier and it always comes down to which option currently has a promotion or sale I can take advantage of.
You do realise that they make the money from locking you into their service? In other countries people pay a lot less than the US.