With ISDN , this changes . Meanwhile , features that were first available with ISDN ( such as Three-Way Call , Call Forwarding , Caller ID , etc. ) are now commonly available for ordinary analog phones as well , eliminating this advantage of ISDN . Another advantage of ISDN was the possibility of multiple simultaneous calls ( one call per B channel ) , e.g. for big families , but with the increased popularity and reduced prices of mobile telephony this has become less interesting as well , making ISDN unappealing to the private customer .