This question is almost the same as this one (Can I send digits to an incoming twilio call with twiml?)
The difference is that I want to hear who is calling party during incomming call before deciding to send digits to the calling party.
E.g. a visitor uses Condo buzzer system's "Call" resident button, that calls the resident's registerd phone number, which answers and observes who is calling and decide to open the door with DTMF key "9"
