Hi,Hello,
Make sure that your 3CXPhone is clean from any configuration accounts ( Settings > Configure Accounts). Now, on you Management Console > Phones you should see a PnP "Phone for Windows" and you PC's IP address. On the top configuration bar click on Assign Ext or Add Ext and do the configuration you want. Also, you can use welcome email method to Provision you 3CXPhone. For more info about this please follow this Link : http://www.3cx.com/user-manual/installation-windows/
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.