The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem (IMS) is an architectural framework for delivering IP multimedia services.
Fiber deployment is becoming popular and is seen as a way to increase a community’s attractiveness to new inhabitants and companies. A new Open Access network is emerging, leading to a more horizontal network architecture. Combining this architecture with IMS enables Operators & Governments to build new services and improve communication needs of people. In fact, it will be completely TRUE to say that IMS is a must-have technology for a Mobile or Fixed Line Service Provider specially if they are going to use Fiber.
Just have a look at below video to get a quick overview of what role IMS plays for Service providers.