intercom automatic switchboard circuit

el0 all. wondered if ne1 could help us out trying to find a switchboard circuit for a 4 way intercom, which can connect 2 handsets upon request by user automatically. if not a circuit which requires manual input will do fine

Auto Intercom

Do the handsets already exist?
if so...Are they two wire or more?
.........What kind of voltage do they require?

How do you envisage the user choosing which of the other three handsets he wishes to be connected to?

How do you envisage alerting someone to the fact that somebody wishes to talk to them (a buzzer?) and is this built in to the handset?

sorry there are 4 handsets (which are built using LM380 amplifier chipsets and the preamplifiers are just basic transistor circuits) which are 2 wire, they will all be linked to the switchboard. If a person wants to contact another handset, they will press 1 of 3 buttons on handset corrisponding to the handset they want, which will alert other handset. The other handset will press buton which will connect the two so they can speak. Im real rookie to electronics, so if u need more info just let us know!