The "Big Four" cell phone carriers in the US -- AT&T, T-Mobile, Sprint, and Verizon -- are now just three, since Tmobile and Sprint have completed their merger. These companies pay big money for advertising, and charge big prices as a result. What most people don't know is that these companies are required to let smaller companies re-sell their services and use their network, often resulting in sizable savings.
These companies are called Mobile Virtual Network Operators, or MVNOs.
My personal favorite is Ting Mobile, which offers tiered rates that automatically adjust based on your usage. You don't have to predict how many minutes or megabytes you'll use next month; instead, you simply pay a small per-device fee, and then depending on whether you used enough minutes to end up in the small, medium, large, or extra-large tier, you pay the cost for that tier. Then your text messages and data usage are similarly added up and you pay a bucket rate for those as well. I'm a person who usually is on WiFi, so my cellular usage is very low and this way I have a full-service device but it costs me less than $30 most months.
Since MVNOs re-sell service on the same networks used by the big carriers, the quality of service is the same. Ting, for example, uses the Tmobile / Sprint networks. Information about the networks used by other MVNOs such as Cricket, Republic Wireless, and Google Fi can be found on their websites.
Of course, everyone has their own usage patterns. Some people use a lot of voice and little data. Some people need unlimited data. Some companies give great individual plans, others have great discounts on multi-line family deals. You'll really need to shop around to find the one that save the most money for your situation. Just don't stop looking at the "Big 3" carriers and think you can't choose a small, innovative company that might be able to pass on savings creatively.
If you spend an average of $40/month on your phone bill instead of $80, that can make a serious difference.