I have half a dozen SIP extensions configured and can make/receiver calls no problem but anytime I try to place a 2nd call to any of them I get 'Busy'. Does 3CX support call waiting? Do you have the ability to ring thru multiple calls on a SIP registration extension? If I use SIP Trunk I can answer multiple calls no problem, but with SIP Registration it seems I can only take one call at a time. Thanks!