Do smaller cell carriers use their own networks?

Episode 1601 (1:40:32)

Gary from Southern California
Spectrum

Gary got an offer to sign up with Spectrum for mobile service, but he just learned that they use AT&T. Do smaller carriers use the big carriers lines all the time? Leo says that the big four is AT&T, Verizon, TMobile, and Sprint. The smaller cell companies, called MVNOs, interconnect and ride piggyback on multiple lines. It's pretty complicated. But if you sign up with a smaller carrier, you're actually running your traffic on the largest carrier.

His Audi car also has internet built in and his service has expired. Is it locked? Leo says it probably isn't. If you look under the dash, at the unit, it probably has a SIM card that can be replaced.