How do you address the issue of device sharing? When I was overseas I worked with prepaid phone cards. The locals would share the same phone, plug in their car

How do you address the issue of device sharing? When I was overseas I worked with prepaid phone cards. The locals would share the same phone, plug in their card code, make their calls, then pass the phone on. As I understood it, the phone owner reaped the benefits of acquiring the unused minutes. Not sure if this is still an issue. But even a "budget" Android phone (sub $100) is a luxury in developing countries. So I'm sure device sharing is still something to consider.