When you say call center, do you mean something like "Cisco Contact Center Express" (UCCX) or do you mean something like "Cisco Unity Connection" (CUC). The wording of your answer makes me ask this and I want to make sure we give you the best possible answer.
In the meantime, one thing to understand is that your phones will not register to either of those application or to any call center or voicemail application. Phones register to Cisco Unified Communications Manager (CUCM). That is the system that will signal with the phone to send and receive calls.
The second thing to understand is that CUCM is the system that will be integrated with UCCX or CUC. CUCM is responsible for signaling to UCCX or to CUC to pass calls and information when phones need to interact with those systems.
This means that whether a phone runs SIP or SCCP is irrelevant for the purposes of passing a call through either UCCX or CUC. And the integration between CUCM and CUC, for instance, can be either SCCP or SIP and any phone running either protocol can still interact with CUC.
Hopefully this helps you ask you next set of questions. We are here to help.
Maren
