Personally, I find phone plans to be a scam, similarly to PCP car deals, albeit you don't pay balloon or give back the phone in the end - perhaps this applies to those swap programs where you have to settle finance before upgrading? Network providers slap high interest rates and inflate their sim deals like crazy.
Anyways, I prefer buying my phones outright and buy a separate sim only deal as it works out cheaper in the long run as oppose to inflated monthly plans with all those extra fees/APRs, etc. Bought a 15P and a 15PM 1TB for myself, straight from Apple and outright. Definitely slapping on cases for both and a screen protector for the 15P due to it being in the handbag and getting all sorts of abuse from keys and what not.