I just got the 5G Gateway.  There appears to be no way to control IP addresses assigned to the devices accessing the internet through the Gateway, therefore each time it is rebooted the IP address for any given device is likely to change.  I have a WiFi enabled music hard drive that is accessed by a couple amplifiers in different rooms to play music from my stored collection.  The access requires a consistent IP address.  Until T-Mobile expands the user interface control to include defining static IP addresses for specific devices, I can not use the built-in router function.  Fortunately you can hardwire an external router that has this function, like any of the Netgear routers.  Unfortunately, the speed of service drops with this approach.  It is still good, but not as good as it should be - dropping from 436MBps to 154MBps.  It's still a lot better than the speeds I had with CenturyLink, but I would like to see T-Mobile upgrade their app to allow this IP address control.  Others have expressed the same kind of need for various WiFi device-to-device communication.