I'm a BSNL Broadband subscriber. I'm assuming that my home wiring setup is something like this:
The main phone line is split into two wires which go to different parts of the house (distant from each other)—one for the telephone and other for the modem. Now, without an ADSL splitter my internet disconnects when the telephone is used (expected).
+-------------> Modem | | Main Phone Line+----->+ | | +-------------> Telephone