You replaced the carrier. From what I understand you havent gotten either of the cards to work in slot 4. Do you have another card of any kind (200,400,308 anything other than the messaging card) to put in slot 4 to test the slot. I know this sounds strange but I had a system relocate and upgrade about a year ago with and older version (4 I believe it was) where I had to populate the whole system to get the messaging card to load.
I know you shouldnt have to do that but that was the only way I could get it to come up. It might be worth a try.