In this measurement study, we analyze whether mobile phone users exhibit temporal regularity in their mobile communication. To this end, we collected a mobile phone usage dataset from a developing country - Pakistan. The data consists of 783 users and 229, 450 communication events. We found a number of interesting patterns both at the aggregate level and at dyadic level in the data. Some interesting results include: the number of calls to different alters consistently follow the rank-size rule; a communication event between an ego-alter(user-contact) pair greatly increases the chances of another communication event; certain ego-alter pairs tend to communicate more over weekends; ego-alter pairs exhibit autocorrelation in various time quantum. Identifying such idiosyncrasies in the ego-alter communication can help improve the calling experience of smartphone users by automatically (smartly) sorting the call log without any manual intervention.