Several mechanisms increase the QoS level of mobile networks thanks to an underlying mobility prediction method (i.e. a means to predict a mobile?s next access router). This paper aims at studying how the accuracy of the prediction method can influence the network QoS in the particular context of call admission control. It shows that (a) the mobiles behaviour must be adapted according to the prediction scheme accuracy in order to achieve good performance and (b) the admission algorithm can be modified to increase its fairness and to give mobiles an incentive to do such an adaptation.