A security mode method (200) receives (210) a layer 3 message in a first domain from a network, determines (220) if the layer 3 message has integrity protection information, ascertains (240) if a security mode has been initiated in the first domain, and forwards (260) the layer 3 message to an upper layer, if the layer 3 message lacks integrity protection information and a security mode has not been initiated in the first domain even if security mode has been initiated in a second domain. This method allows a mobile station to process a non-integrity-protected layer 3 message from one domain even if integrity protection has been initiated in another domain. When packet-switched and circuit-switched connections are being concurrently set up, a non-integrity-protected message in one domain may arrive at a mobile station after an integrity protection initiation message in another domain.