Bernard Peek wrote:

What you want to do really needs some sort of computer system.

The VoIP adapter I suggested has all the intelligence required.

The cheapest way of doing it would be to use a Raspberry Pi costing
around £30 but you can get an awful lot of phone calls for £30. Will
it save you that much?

If you happen not to make the required two chargeable calls per month,
they charge you £1.50/month for not making the calls and £2.70/month for
the otherwise-free caller-id.