Unable to setup port forwarding with LM1200

Has anyone been able to setup port forwarding on a new LM1200 with current firmware? Have tried with only the LM1200 with a T-Mobile SIM Card and have tried adding a new router and not able to port forward. Have tried a second new LM1200 and am unable to port forward with both of the LM1200. Need help as all documentation shows port forwarding should work?