Hello! I do that route every morning! The service is good from Peckham Rye (no service going through Denmark hill tunnel and sometimes flaky at the actual station), all the way until you enter into City Thameslink, then no service until the second set of escalators when leaving St Pancras station!! I usually listen to the radio, when there is no service, i'm checking my emails which have downloaded to my phone...I suspect people are doing the smae or watching video content or playing games.... I've not really seen people taking calls though.