I've had cell phones / smart phones on three of the four major carriers over the last 15 years (never been a Sprint user). In the last few years, there has been a significant increase in what are known as MVNO's (Mobile Virtual Network Operators). In a nutshell, a MVNO is company that purchases "very large" quantities of minutes and data from a major carrier and then re-sells them to consumers. The major carriers benefit by having their networks being in a "sold state" (they are bringing in revenue), the MVNO's benefit by making money on the resale to consumers, and the consumer benefits by being able to purchase services at a much lower cost than buying direct.
Typically, MVNO's operate as pre-paid wireless services so that there's no "bill collection" to worry about. You don't pay, they shut you off. Less overhead on their part which helps them keep costs down.
I moved my services from an AT&T post-paid account (the more typical type of account that we mostly have been used to) to a Straight Talk pre-paid account about 18 months ago. My daughter did the same thing three and a half years ago.
I cut my bill almost in half when I made the move and gave up pretty much nothing in the process. I still use AT&T services from AT&T towers (exactly the same as before) with a couple of "frills" removed (I can't use my phone as a hot spot any more, but I almost never did this anyhow).
Straight Talk has a rewards program that you can join and you can earn points with them that you can redeem towards things like a free month of service. They are running a promo right now that will net new, referred users a free month of service (via earning enough points for a free month). If anyone has been thinking about switching their service and might be interested, let me know and I can get you the referral.
Happy to answer questions about making sure you can switch, what you need to do, etc.
Disclaimer: As the referrer, I would also get a free month of service.