Here is the Sprint sim Card SIMOLW416Q - is valid for S8, S8+, and Note 8
If Sprint is much better in your neighborhood than AT&T, that should be the way to go. The above part number will work with Note 8. Yes you start with the /BYOD to activate a Sprint phone. Best to have the SIM in and its ICCID ready when asked. There was a special on BYOD Jan 1, may still be valid. https://www.freedompop.com/byodpromo9
99c instead of $20 - but I think you have to accept a trial paid plan and trial paid services bundle for first cycle. As usual, you can downgrade to FREE plan and NO services any time.
If AT&T better where you are, then that is way to go. Need a FreedomPop SIM. When ordered from FreedomPop, they arrive already activated. Just follow the instructions of setup and start using your phone setup for GSM access.