1. A system for processing requests, the system comprising: one or more processors; and a memory coupled with the processors and having stored therein a sequence of instructions executed by the processors to execute: a first layer comprising a plurality of applications that provide telephony control features, the plurality of applications comprising an application dispatcher; a second layer comprising a plurality of abstract call control enablers comprising: one or more call control enabler interfaces; one or more Application Program Interfaces (APIs) providing an abstract interface for invoking a plurality of call control functions, a third layer comprising a plurality of call control enabler instances that provide adapters to network resources to provide the plurality of call control functions, wherein one or more of the call control enabler instances are instantiated in response to one of the plurality of applications invoking one or more of the plurality of call control functions through the APIs; and a fourth layer comprising a network layer of a plurality of network resources that are each coupled to corresponding ones of the call control enabler instances; wherein the system is configured to perform operations comprising: receiving, by the application dispatcher, a Session Initiation Protocol (SIP) request; analyzing, by the application dispatcher, the request to extract a plurality of Uniform Resource Identifiers (URIs) to process the request from a header field of the request; dynamically determining, by the application dispatcher, a first application to process the request based on a first URI in the plurality of URIs in the header field, subscriber profile information, and one or more policies, wherein the determination is made in the first layer; routing the request to the first application to process the request; receiving a response from the first application after processing the request; dynamically determining, by the application dispatcher, a second application to process the request based on a second URI in the plurality of URIs in the header field, the response from the first application, the subscriber profile information, and the one or more policies; and routing the request to the second application to process the request.