1. A method of caching media for use in a telephony application comprising: at a call router, generating a media request initiated by a telephony application session, the media request specifying a requested media resource through a persistent Universal Resource Identifier (URI); sending the media request to a media layer; where the media layer performs the following steps: checking in a cache for a telephony compatible audio media resource specified by the media request and identified by the persistent URI; if a telephony compatible audio media resource is identified in the cache by the persistent URI, forwarding the cached audio media resource to the call router, if a telephony compatible audio media resource is not identified in the cache by the persistent URI, processing the media request at a media processing server according to the persistent URI of the media request to generate a first telephony compatible audio media resource, storing the first telephony compatible audio media resource in the cache as a resource specified by the persistent URI, and forwarding the first telephony compatible audio media resource to the call router.