Windows 10 Pro Gsm Pack -

In essence, this pack enables a Windows 10 Pro device to behave like a smartphone. It unlocks the operating system’s ability to:

This feature is only available on Windows 10 Pro, not Home edition. Also, your device must have an integrated cellular modem.

There is no "Windows 10 Pro GSM Pack license key" sold in retail. It is a binary component—you either have the hardware to support it, or you don’t.