Please Answer your phone

Help needed to understand what I have please.
Back ground Info:
I have the Reolink Go and the Reolink Go PT. I am unable to activate them due to no SIM card. I believe is my issue. When I bought them my goal was to obtain a cellular service through AT&T for $40/month and be able to use the camera where ever I traveled not worrying about having WiFi access available to me or not. My regular cellular service is through Verizon and not wanting to give that up. I believe my option is to take out an additional unlimited plan with AT&T.
Questions: Do I have to have a Sim Card for each of my cameras OR would I be able to use these specific Cameras Reolink Go and the Reolink Go PT through a NVR box? Not sure if the NVR box accepts a SIM card but that seems like if so it would allow me to use multiple cameras through it. Please help me understand how this works. Reolink not answering their phones.