Looking for a similar solution, I had one Huawei USB 3G stick lying around and used that with RPI 3. Everything worked just fine but after a couple of days it would randomly disconnect and wouldn't restore the connection so currently, I am looking for some 3G/4G router to do the same job.
When I moved into my new house but the internet fiber was not yet activated I also used a Pi with a Huawei 3g dongle as gateway for my home. Most expensive internet I had to use for 3 weeks.
Didn't have any reconnects though but I had a script running checking the connection and if it failed it would re dial
