NG IN platforms have SIP and IN capabilities, how are service brokers being used in the market?

If the service provider is writing applications from scratch (starting over?) then an NG IN platform will indeed provide interfaces to both SIP and IN worlds; existing applications will likely not be able to interact with the new ones. In contrast, service brokers enable new composite / blended service creation by utilizing existing application and combining their capabilities; think PrePaid with Closed User Groups or VPN and FindMe/FollowMe. Service brokers also enable the extension of existing applications to new networks, without requiring code changes; enabling new application to be deployed on old networks and old applications on new networks. Service brokers may also provide additional functionality, such as IN-IN trigger management, SCIM, Web 2.0 gateway capability, and Media Resource Brokering.