A method and system are provided for optimal routing of calls in an Internet Protocol-based Base Station System (IP-based BSS), whereby a plurality of new messages are introduced on the A-interface. One such message informs the BSS that the Circuit Identity Codes (CICs) included in the message can be connected to the BSS to provide optimal routing of one or more calls. Another such message informs the BSS that the CICs included in the message are to be restored as separate CICs on the A-interface. The provision of such messages overcomes the significant disadvantages of the existing and developing BSS implementations.