1) You can use iPhantom on any device that you own or control provided you are the only person using these devices and they are not used simultaneously.
2) In the event of simultaneous use or use on more than one device by multiple individuals, each device requires a separate license.
3) Apple requires a separate Apple Account to be setup for each license that needs to be purchased.
The above is in line with Appe’s Commercial use policy quoted below.
“Individuals acting on behalf of a commercial enterprise, governmental organization or educational institution (an “Enterprise”) may download and sync Apps for use by either (i) a single individual on one or more devices owned or controlled by an Enterprise; or (ii) multiple individuals on a single shared device owned or controlled by an Enterprise. For the sake of clarity, each device used serially or collectively by multiple users requires a separate license.”
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