Andy,
Cellular providers in the US provide you with a private dynamic IP address. There is no inbound access over this type of connection. Even if you try to use dynamic hosting, lookup the IP, etc, you can’t remote in. You’ll need to ask your carrier for a static IP address. This gives you a routable connection and you can come in over it just like a land line connection. You can then port forward, establish your VPN, and more, as your connection will be unrestricted.
Keep in mind, carriers do charge a fee for this. Verizon charges a 1 time $500 fee for the account. The good news is you can apply a static address to additional lines on the account without paying again. Other carriers may require a monthly fee, some form of business account, or a minimum number of lines.