Yup ! 100% correct, unless BT change your master socket and put a microfilter in there which means that your ADSL modem HAS to be plugged into the master socket, and all other telephone sockets can ONLY be used for telephones/faxes/modems/sky, etc...

Usually, if your installation is Wires Only, you get the microfilter thingies because BT don't visit your house, if they do come and change things, you shouldn't need any.