The signaling system 7 (SS7) is the control network used by public telephones all over the world. Having been designed in an era where few large companies controlled the entire network, SS7 has virtually no security. Due to telecommunication deregulation, liberalization of economies and the convergence of telephone, IP and wireless networks, interfaces to SS7 have increased. We show how these deficiencies can be exploited to isolate or shut down telephone switches. As a solution, we propose MTPSec - a framework that enforces authentication and custom creates secure channels at the message transfer part level 3 (MTP3) layer. We show by simulation that employing MTPSec adds only 360 /spl mu/ seconds to an average call setup time delays to a domestic telephone call in an average sized country. It is quite tolerable for getting an additional security service given that the current connection delays are between 2.0 to 2.5 seconds.