3PCC Cisco phones

Hi guys,

Would really appreciate some help on this one. A client ordered CP-7841-3PCC & CP-8865-3PCC phones. Today he comes back to us saying the 3PCC firmware is not compatibale with ''Cisco Unified Communications Manager (CUCM)''. After searching the internet for a couple of hours i did not get any wiser. Is there a way we can make this work? or is there a way to Change the firmware on the phones to 'K9' so it would work?

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Thanks in advance!