Why wouldn't it be possible?
The phone is providing the client app connection, you just need an interface from the client to the POTS system, or just the hardware you're using as a phone.
Years ago I had a cordless phone that connected to the Skype client on a pc - you could call a phone number, or a Skype contact with it.
This is no different - you just need to establish the interface between the hardware and software.
Hahahaha