Well I got TMobile and the EdgeRouter working today. It wasn't all that easy. Biggest issue was changing the DHCP for the EdgeRouter to use a subnet that was not going to be used by Tmobile or my other Internet provider. Once that was squared away and I added rule sets to allow traffic IN via the LAN port it pretty much all worked.
I can turn off the copper Internet modem and the EdgeRouter picks up on that fairly quickly. Not sure how well it will pick up when the device is working, but going nowhere though. :)