A method and system for dynamic queuing utilizes a SIP messaging structure within a call center's architecture for interacting with a caller. The method and system can be used for ACD services developed for IP telephony using SIP as the signaling protocol. A SIP subscriber can also interact with an ACD system in the Public Switched Telephone Network (PSTN) work space. In the latter case, a PSTN-to-IP gateway carries the bearer path and call level signaling between the two spaces, and corresponding Computer Telephony Integration (CTI) signaling links are used for linking the ACD specific signaling between the two spaces.