Home Internet Static IP

The ~20-hour ordeal that I had to go through for all this is worth a separate writeup, but yes, you can get a static public IPv4 address on your T-Mobile gateway/router. Here are the requirements:

1. Set up a T-Mobile Business Account using a Federal Tax ID Number (also referred to as an “FEIN”). Tú no se puede set up the business account as a sole proprietorship under your social security number (SSN). You’ll have to do this in a physical store.
2. Ask your in-store sales rep to add the following add-on to your account:
   ZSIPV4MI "Bus Static IPV4 MI $3 Chi"
   That is the product code / SKU for a static IPv4 address for an extra $3/month. (There's a similar one for IPv6, if you need that for some reason.)
3. Make sure to request an Inseego FX2000 device as your gateway/router. They are unlikely to have these in-store. (I had to do a horrific rigamarole to get one of these by calling Business Sales ahead of having the right kind of business account set up.)
4. Call Business Tech Support and request that they finish approving/activating/provisioning your static IPv4 address.
   I wish I could give you the direct number, but every time I call what I'm previously told is a direct number, I get bounced around to 4 or 5 reps before getting to someone in the right department. You can try Business Customer Care (allegedly +1-888-310-8369) and then make sure to specifically request Business Technical Support who can help with 5G Home Internet.
   9 out of 10 "technical" "support" reps are not going to know anything about IPv4 or IPv6 or static IP addresses or anything. You will likely get a lot of runaround and misinformation. (Do not be fooled by claims about having a "Retail Business Account" versus a "Corporate Business Account" or the line needing to be on some other kind of plan (eg, ZUNLINTTR); these are all irrelevant!) What I found ultimately had to happen was for them to update the APN associated with my line and then for me to power cycle my Inseego FX2000 gateway for it to pick up the new settings (and then it automatically configured itself with the static IP address, which I was able to find on the administrative configuration website of the router itself).

A few other notes:

• You do not ever need to use the T-Mobile Internet app on a mobile phone, no matter what anybody tells you.
• If you have your own router, it might be tempting to set the Inseego FX2000 to “IP Passthrough” mode (under Settings → Advanced → LAN), so that your own router gets the public IP address (and you avoid being double-NATted), doing so will prevent you from being able to access the Inseego FX2000 configuration website (since it won’t have its own IP address to access via your browser), and you’ll lose access to some useful diagnostic information.
  So I recommend against IP Passthrough, instead opting for putting your own router in the Inseego FX2000’s DMZ (under Settings → Advanced → Firewall), and to do so, you’ll probably want to configure your own router to use a static IP address on the Inseego FX200’s LAN subnet.
  From a performance perspective, I have it on good authority that the biggest introduction of latency is the mere fact of there being a physical device, rather than the double-NATting itself. Putting your own router in the DMZ should address any of the functional downsides of double-NATting.

I can confirm that with all of the above, I'm able to access internal network services on my private LAN with the appropriate port forwarding set up. For example, I have a machine I SSH into that only has a private LAN address, but when I try to connect to it from outside my network through my T-Mobile static IPv4 address, the Inseego FX2000 forwards all traffic to my own router (which is in its DMZ), which then forwards the specific port to the machine I'm SSHing into.