We have a Mitel 5000 that has 2 SIP Trunks that are connected to a Quintum Gateway. Incoming calls come through just fine, but they are not able to put the call on hold or transfer the call they get a message saying "Destination is not Responding" Also they are not able to make outgoing calls, they get the same message. We have opened the necessary ports on the firewalls at both ends, but still makes no difference. Any solutions??