Missouri is AT&T country, both cell phone and internet, but dealing with AT&T directly frequently stinks. Fortunately, it's usually cheaper dealing with AT&T services using a middleman to deal with them for you, with fewer hidden fees.
Toast.net for fiber/vDSL internet. Plans start at $60/month for 100/100Mbps, $50 install, friendly people from Ohio with support and sales, free router with a year contract, grandfathered pricing, no data cap, all in with no hidden fees. AT&T's direct promo pricing will look tempting, but read the fine print and how they handle pricing. The savings first year going directly with AT&T is minimal at best, and a losing proposition of constantly fighting to lower your bill to a reasonable rate after.
Red Pocket GSMA for cell service, plans start at $10/month $20/month (edit: correction, $10 plan is GSMT only as of this morning apparently - GSMA starts at $20/month or $15/month [$180/year] if annual plan purchase). Any AT&T branded VoLTE capable handset should work in theory, locked or unlocked. BackMarket is a good source for refurbished handsets these days. Swappa, Glyde and Gazelle are okay for used as well. If you go Android, Motorola and Nokia are decent. And yes, you'll probably have to buy new cellphones, because all our pre-4G-LTE common global roaming networks are being shut off next year, and LTE service bands are a shotgun of a hot mess with very little cross-network interoperability... especially with voice service.