Hi Mojo

Prior to DSL lines , the data was provided through the normal telephony lines which limited the simultaneous use of voice and data services, later in the DSL technology both can be used simultaneously using a DSL modem. This is possible by transmitting the DSL signals at a different freq than the vocie signals. This splitting of the analog signal can be done via a splitter ( a tiny box, with 1 RJ12 input and 2 outputsports).
From the dagram below, you can see that a CPE (customer premises equipment) typically your home modem is connected to the DSLAM . Mutiple such DSLAMs would then feed into the aggregator which form the core network of any given telco. The DSLAMs are huge racks or say switches which are existent in the local telephony office. Though we say it as a digital subscriber line, the access network ot the DSLAM is still analog and hence we need a ADSL modem.
The underlaying core network can be anythign such as ATM network , A frame relay network or MPLS network

Nice explanation. Thanks.