The present invention provides a method involving a femtocell in communication with an Internet Protocol Multimedia Subsystem (IMS) network. In one embodiment, the femtocell operates according to code division multiple access (CDMA) standards. The method includes receiving, from the femtocell and at a first secure entity in the IMS network, first authentication information generated by the mobile unit using a first random number broadcast by the femtocell in a global challenge. The method also includes receiving, from a second secure entity in the secure network, at least one security key formed based on the global challenge and second authentication information for uniquely challenging the mobile unit. In one embodiment, the second secure entity is a CDMA-based authentication server. The method further includes providing the security key(s) to the femtocell in response to authenticating the mobile unit based upon the second authentication information.