Comment by dilyevsky

IMS is just SIP core + bunch of gateways + integration with base LTE infra (eNodeB, PCRF, etc) so "signaling messages" are just SIP messages. So depending on whether those compromising headers were included on things like SIP 180 Ringing messages and such it may not be enough to not answer the calls. Source: actually worked on deploying IMS at a telco (not this one)