If a person's mobile phone was designed to work with $4G$ technology, what will happen when a $5G$ network is rolled out in their area?

They will still have service through the $4G$ network for at least several years.

Their phone will automatically upgrade itself to work with the new $5G$ network.

They will lose service as the $4G$ network is deactivated to make room for the $5G$ network.

Their phone will only work when they are out of range of any $5G$ networks.

I don't know this yet.