The most important challenge for the implementation of the Future Internet is to make the heterogeneity of access technologies transparent to the end user. Compared to the general case where the interworking networks are independent, the case of femtocells interworking with pre-existing wireless networks poses more challenges due to the sharing of the same backhaul capacity. Therefore, while a user is practically able to initiate the same service through multiple network interfaces, he is allocated capacity from the same capacity pool. However, while the femtocell inherits the QoS mechanisms of cellular networks and is able to provide a reliable CAC, this does not apply to the IP-based networks and that may drastically affect the performance of the femtocell. Hence, we propose an integrated Dynamic Service Admission Control (DSAC) framework for coexisting femtocell, wireless and wireline network environments. In particular, DSAC is able to provide QoS guarantees as a conventional capacity partitioning scheme while at the same time offers better performance in terms of acceptance probability and capacity utilization especially when short term variations of traffic load composition occur.