ach for fixed-mobile convergence (FMC) deployments [5] because the IMS is access independent, which means that the same systems can be used for both main types of access networks, fixed access and mobile access. Also, the 3GPP continues with the development of the IMS and its functionalities in further releases after Release 8, which defined the common IMS version [6]. The IMS uses standardized IETF protocols, of which the most important (for the IMS) is SIP [3], as the signaling and control protocol for different services, including multimedia session services (e.g. voice and video telephony services provided by tele- com operators) and some non-session services (e.g. message exchange services provided by telecom operators). Overall, the IMS uses SIP for signaling in the same manner as PSTN/ISDN (Integrated Services Digital Network) were using SS7. However, SS7 (in the past) and the NGN framework (at the present time) are standardized by the ITU, SIP and the Diameter protocol are standardized by the IETF, while IMS itself is a 3GPP standard. So, we have three different SDOs with synergy in provision of a common IP networking environment for legacy telecommunication services such as voice services. In practice, the IMS was initially used for voice services in fixed networks in the first half of the 2010s, and then in mobile networks in the second part of the 2010s. Although the IMS can support a wide range of services and there were efforts for such innovations by major telecom operators during the 2010s, it appears that telecom operators (telcos) cannot match the pace of OTT service providers (e.g. Google, Facebook, Amazon) in the innovation of Internet-based services for end-users (human users). So, although the IMS provides an environment for many new services, it has arrived on the market later and telecom operators usually have longer time from innovation to the market (due to different reasons, such as legislation in a given country, the need to have a sustainable business case, having a big corporate hiera