You can also use Phonein as an inner door access solution for your residence/office, if the inner door to your residence/office is a strike lock. For this to work, you will need to connect/integrate Phonein with the strike lock.
To install Phonein Intercom for apartment door access:
When using Phonein for inner door access, it must be connected to power. Since Phonein can draw power from the same wires connected to the strike lock, this should not be a problem.