For SIP phone service, there are generally two options: 1) add new features to a legacy PBX or 2) select the full VoIP deployment from Internet2's SIP services on the Mitel Clearspan service. If option 1 is selected, SIP tie trunks are put in place between your existing PBX and the Mitel Clearspan service (additional fees apply for tie trunks). Routing between the two systems will need to be set up and tested. If option 2 (preferred) is chosen, numbers and extensions are assigned, phones are shipped and deployed and users can begin using the services immediately. Hybrid scenarios (a combination of both options) are also available.