ADS-B is not necessary for international overseas flights, but it is mandated in Australia, above certain flightlevels over Hudson Bay in Canada, and in few other areas in the world.
You're absolutely right. I live near Houston so I confused that rule with the Gulf of Mexico rule. Flights over the Gulf are required to have ADS-B.
Most new aircraft have an ADS-B capable transponder, and in most cases the ADS-B function will be active. This it not something that is decided on a flight by flight basis, it's basically off or on (you can't switch it from the flightdeck
AFAIK, unless you switch the transponder to off).
This may be true, but I'm curious to why if they have the equipment, why only transmit your altitude and nothing else such as lat/long, spd, callsign.
And yes, I have a miniADSB