Red Pocket cellphone plans

https://redpocket.com/plans

They let you use phones from any of the major networks. They provide a different SIM card depending on which network your phone works on. For Sprint's network you don't even need to change your SIM card.

They offer unlimited text/talk/data with up to 5GB LTE data for $30/month with auto-refill at the above website.

If you buy a year's worth at a time, you can get cheaper per-month prices for the same plan - $20/month or less.

The yearly plans are only available from eBay (or Amazon, but Amazon has fewer options than eBay). There are so many different ones listed on eBay, that it is rather confusing.

This is a non-renewal one for unlimited everything (5GB LTE data) a year at $18.75/month
https://www.ebay.com/itm/132544686405

This is a yearly renewal one for the same plan at $20/month - I'm not sure why it's more expensive:
https://www.ebay.com/itm/20-Mo-Red-Pocket-Prepaid-Wireless-Phone-Plan-Unlmtd-Everything-5GB-LTE/132858308694

This is a single month for $30:
https://www.ebay.com/itm/30-Mo-Red-Pocket-Prepaid-Wireless-Phone-Plan-SIM-Unlimited-Everything-5GB-LTE/131953089331

It looks like the difference between the renewal & non-renewal ones is only whether or not SIM cards are provided. But I'm not certain.

I'm not sure if (I don't think that...) the color of the cards means that they are limited to a certain network, but in one of the above links, it does correspond to which network's SIM card is included. So pay attention to that if ordering them.

If you don't want unlimited everything, they also have other cheaper plans available.

Here's a review from a year ago: Red Pocket Mobile Review