Unfortunately noone cared to pick this project otherwise we could have seen many interesting telephony related projects based on this idea e.g arduino based 4 port pbx its like arduino telephone exchange but none is interested
I tried to contact few shield venders they gave me estimated price of 1000 to 1200 USD which I cannot afford
Anyway whoever want to peruse please note along with modem chips CONEXANT also provide a complete circuit diagram for reference modem CSM92 ,all you need to do is to combine CONEXANT modem with Arduino