I think you stumbled on my next choice. If there isn’t already a commercial solution, then I may see about making a small PC that had those as interface cards, or maybe I could find USB interfaces and connect it to a raspberry pi or something. It means that it might be a slightly bigger box than a commercial solution, but it would be one contained box.
The other appealing aspect to this is being more controllable. If I have a raspi with a cable connection, DSL or dailup connection, and a USB connection to a cell modem I can easily hardcode it to go through cable if it has internet connection, then try DSL, then cell if the others aren’t working. Saving myself unnecessary data charges. That could be a very interesting box. Just take it wherever and keep all your possible WAN connections on it. Even make sure you have regular Ethernet and T1 uplinks on it.