LineLink doesn't work with T-Mobile 5G home internet router

I am talking about the new Tmobile home internet service/device.  Does not support VOIP.  I dont know about the older white boxes.   Sales says they do support, tech service and actual testing says VOIP does not work.   There are no controls to the gateway that we have access to.  There is no DMZ to put your VOIP device in etc.  Zero admin controls on the new internet device they are shipping.   I have Vonage and it did not work with the new grey tower gateway tmobile provides.   Would love to have a solution so I dont have to cancel.