I'm guessing you're with ATT? From what I've seen on HowardForums and Reddit, it's working for many, but ATT users with Intel modems are having the most issues.
P.S. For your googling pleasure, "field test" or "field test mode" will yield more results.
I wanted to use this again since I had it on my 6s plus. But with the 7 plus, it will not connect. I have AT&T. I've tried several times over several different days, still, no connection