<qa>  What is the trial of superiority for the first phase?Two SMS interventions will be tested which will correspond to different phases of the OBCS invitation procedure. This sequence of interventions leads us to perform three interlinked trials: a trial of superiority for the first phase intervention 1: sending an SMS a few days before the initial mail invitation, then two non-inferiority trials for the second phase intervention 2: sending an SMS in place of the first postal reminder. 