I have a bsnl landline no. The line is connected to two parallel phone sets at the ground and first floor respectively.How can I use these phones for internal communications between two floors ???basically the line is divided into two using splitter and then each output of splitter goes to a filter and each output of each filter goes to a modem and a phone respectively.This way i have 2 phones and 2 modems connected to single bsnl line. Now i want to know how to create intercom between the phones on 2 floors??I dont know where else to post this thread ,so please move to respective section if it doesnt fit here.