In the absolute way yes you can use 2, 3 or more ways to go to the Internet. Of course.
You only have to set up different routes for each access and keep the default route on one of them. But in this case, if this configuration is permanent, it's recommended to get a Autonomous System.
In the relative way of the N770, if you want to set up 2 Internet accesses you'll have problem if you use the standard connection system the last access set up so the last default route set on it will win. If you want a usable system you'll have to set up your routes manunally. But what can be the interest in doing such things with the 770 ?
To make it a router between 2 wireless worlds ?

db