Integrated Cellular Networks (ICNs) are normally constructed by adding ad hoc overlay on cellular networks to solve the latter's flexibility and capacity expansion problems. In such networks, routing plays a critical role in finding a route to divert congested traffic from a congested cell to another less crowded cell. While much work has been conducted on routing protocols in ICNs, no dedicated work has been found for an important aspect of routing, namely source selection. The process of a source selection can be an algorithm which is designed for selecting a proper pseudo source to releases its occupying channel to a blocked mobile user. Consequently, this pseudo source diverts its ongoing call to another cell by using a free channel in a neighbor cell via a relaying route. Based on an introduction of a representative ICN infrastructure, this paper proposes three source selection algorithms. Both numerical analysis and evaluation results are presented, which show the efficiency of the algorithms and their different ability in adapting to different network situations, such as traffic density and cell capacity.