Ooh, that’s an interesting idea. Not sure if it exists - using my Treo years ago as a Hotspot was pretty challenging, and it was an early smart phone.
Many laptops today have a SIM slot - just get a cheap data plan. You can also get a cell card that plugs into USB. Back in the day we had PCCARD slot cell cards. That was nice.
Xfinity had a deal when we switched from Verizon - a data-only Sim for $10/mo that uses the shared data on our plan. Great for the iPad.