Hi Raghuveer,

I don't know the standards for Caller-ID in India (sorry), but there must be a national standards organisation that can help you.

You should check out Zarlink (formerly Mitel). They have a range of Caller-ID circuits for every standard in use. Maybe they have some info on the standards used in India as well.

When a call is answered, a current will flow and the DC voltage on the line will drop from around 48V to around 10 - 15 V. Both these conditions can be easily detected.

Best regards,
Rob Klein.