Here’s a low-cost two-way intercom circuit with musical ringtone that can be made using readily available components (see Fig. 1).
Melody generator IC UM66 (IC1) generates ringtone for this circuit. The supply voltage to IC1 is limited to 3.3 volts by the zener diode. IC LM386 (IC2) amplifies the signal received from either the condenser mic or the output of IC1. The speaker volume is adjusted with the help of VR1.
For two-way intercom operation, make two identical units as shown in Fig. 2. The output of one unit goes to the speaker of the remote unit, and vice versa. If you use separate power supplies for the two units, a 3-core cable (two wires for outputs and one wire for common ground) is needed for intercom connection. The wiring for intercom is shown in Fig. 2.
The two units can be housed inside separate handy phone cabinets or toy cell phone cabinets available in the market.