Call transfer issues

If you are having trouble transferring calls it may be a result of an improperly set prepend digit.
Verify both the client settings and the server side setting.

Client

Server

However, if the prepend digit is not the issue, it may be a gateway configuration issue.
Especially if you are trying to transfer a call you put on hold.
When handling a held call, we don't actually transfer the call.  We do a redirect.  This allows the call to retain all of the original call information and not be stamped with the operator's information.
The trouble is in that original call did not have all of the correct information to begin with.
Confusion arises because you cannot actually recreate it with a physical phone since you cannot actually perform a redirect on phone.

You can test this by performing the the same Call->Answer->Place on Hold -> Transfer process with a call that originates from another internal extension.  It should complete as expected.

This problem and fix resides on the gateway configuration.  The fix is phrased somewhat differently depending upon the gateway type (MGCP, ISDN, H.323,SIP etc) but its the same logic.

Select the box for Redirecting Number or Redirecting Diversion Header Inbound/Outbound.
This change will require a Gateway reset, so you may need a maintenance window.

More information can be found here.
https://supportforums.cisco.com/discussion/10926046/call-forwarding-retain-redirecting-device-information