The mfgr must have negotiated something with one of the cellular carriers to give them unlimited access for a fee, with the stipulation that it's only used for these occasional OTA updates which really don't use much data.

However, I must point out that a satnav device's occasional updates, as I said, don't use much data: just a multi-megabyte download every few months at most. But streaming constant surveillance data from a TV to the "mother ship" is going to require far more data than that. Multiply this by an average of 1-3 TVs per household, and this seems like a big load on the cellular system.