You’re talking about MVNOs which buy access wholesale from big networks and resell to consumers. Mint does this with T-Mobile and they offer a good deal for the price - call quality should be fine, but customer service will necessarily be variable.
The cheapest MVNO that piggybacks off T-Mobile’s service is Tello.
If you’re happy with T-Mobile service they run two MVNOs themselves: Boost and Metro. (AT&T owns Cricket, and Verizon owns Visible.) If you’re concerned about customer service those are probably the best bets.
(I’ve been using T-Mobile for years in NYC and it’s fantastic here. Paying around $80/month for one line with unlimited everything plus included iPhone hotspot. Not cheap but for me ultimately worth it.)