Red Pocket owns them now. It's on AT&T. Don't know if they block hotspot, but if they do then just use SecureTether if you're on Android - works just fine on AT&T last I tried it early this year. When I was an RP customer a couple years ago, they had no problem activating hotspot for me when I called and asked.
Calls using the app, https://play.google.com/store/apps/details?id=com.unrealmobile.unreal, use VoIP so either cell data or wifi. SMS is not available in the app, so that is not sent over data. Calling from the regular android dialer does not use data either.
SIMs and Sprint have always been weird in that they are linked to the phone. I was not prompted for one from Unreal Mobile. As part of the qualification process they asked me to put in the ICCID, so I don't think you can sign up without one. You would have to buy a CDMA one from Ting ($9), Twigby ($3.99), Tello ($9.99), TPO ($6.99), or Boom! Yellow ($4.99). From before, I only have dealt with Ting.