If a device gets an identity, how can that be used in the real world?

For example, if you have a cell phone, this phone has a unique number, which is called the IMEI, the International Mobile Equipment Identity. That identifies the device. It is printed somewhere in the hardware, so you have an identifier already. You could then start linking it up to more and more credentials which say if I use this cell phone then it can open a door, for example. So that would be a credential that could be added to your cell phone while the cell phone itself is identified by an identifier.