We have plenty of Cisco CP-7821 phones, and our organization want to implement a open source Elastix Software (v2.5). i have installed the system and configured it, but can't configure the telephones to connect to it. the phones keeps telling me (phone not registered). i've updated the XMLDefault, DialPlan SEP file to match my server, TFTP server, and downloaded the firware (from the current one to the latest one) with no luck.
Does anyone have whats required to make the 7821 function on Elastix? its been a week googling with no luck. instructions or steps to solve it is highly appreciated.