Cisco routes have broken NAT when it comes to handling SIP traffic. The resolution for this problem is the following two lines of code to be placed within the Cisco router, Note this is ONLY required if the router is handling NAT and IP phones reside behind said NAT.
no ip nat service sip tcp port 5060
no ip nat service sip udp port 5060
Once these two lines are placed please write to the config and either clear NAT or reboot router for the changes to complete.