@WoodshopHandman Some services like T-Mobile allow for third-party phones, like the kind you buy from Walmart, even if the official store only has a specifically allowed set. You have to look at each specific third-party phone though and what other people say.
@WoodshopHandman Most of the mvno carriers will let you bring your own device. China makes a ton of globally compatible phones. Rugged style dumb phones? Ali Express. Just make sure it has the bands you need. It's hard to get a full on "dumb phone" because sms is kind of the old standard so a lot of cheapo ones throw in WhatsApp even in dumb phones, but you can disable it usually. This one is like $22 with two US reviews on AliExpress.