But Admiral Patrick (sorry, I still don’t know how to link/tag users) wrote he has to scan and email the physical signature from the paper, so it is not really physical anymore? Maybe he has to send the physical paper by snail mail in addition to the email.
If you happen to have a Fritzbox with VoIP capability it contains a SIP server and you can register SIP clients on it (e.g. Fritz App Fon, linphone, twinkle) and use them to phone internally.