Here's an example from 2025 with a major US carrier - Verizon: https://tech.yahoo.com/phones/deals/articles/want-free-iphon...
They run various schemes like this all the time, you can also trade in your existing phone a lot of times for pretty favorable terms. I've traded in phones that were a few years old and gotten $1000+ for them, especially when switching providers.
Verizon's "free" iPhone deal is you pay for the phone up front and then receive a bill credit. Here's the fine print from one of those deals:
$729.99 purchase on device payment or at retail price required. New line req'd. Unlimited Welcome, Unlimited Plus or Unlimited Ultimate plans required. Less $730 promo credit applied to account over 36 mos; promo credit ends if eligibility requirements are no longer met; 0% APR.Taxes & fees may apply. Credits will appear on your Verizon Wireless bill.
That's not free except at point of sale.