I have no doubts about it, and that's why I won't deal adding 3G/4G connectivity features to the server itself but I'll use an appliance.. ideally, I can connect to wan with any kind of link.. my server will find all of them on a eth interface.. at the end, it's just a route/gateway, no matter how I connect.
to be more specific: in some environments, we use an ADSL router, but we have backups on an ISDN line, a 3G router and finally on a satellite link..all of them are on a different eth interface.. if tomorrow I want to upgrade my 3G router with a 4G one, it's a matter of seconds.. and all the system is reliable, stable, available..
if you need a wan backup, use the right tool in the right place at the right price.. reinventing the wheel is not a good idea