I'm posting this in the interest of sharing my recent experience. Additional comments/replies are welcome and maybe should save someone out there the same headache.
I have had my Network Extender (NE) for over two years. And I knew that I could tell if I was attached by dialing #48. All lights were blue, and when I tried calling the #48. A message said it was an invalid number.
After calling customer support, and having very difficult time getting the rep to understand the problem, I finally got transferred to tech support (25 minute wait). Turns out Tech Kevin understood and knew exactly the problem. He explained the the NE did not have HD Voice compatibility and that the message that I was getting was because the NE could not ever pick up the call unless the HD voice is disabled on the phone. I tried his suggestion using our other iPhone which I had also activated HD voice. I set it back to Data only. And then the #48 worked and it said we were on the NE coverage.
Kevin was great! Unfortunately the customer service rep, didn't understand the issue, but would not admit it. She suggested that I reboot the NE. and at one point asked me the phone # of the NE. This is such bad education and judgement. If they don't understand that admit it and transfer me to tech. After 20 minutes, I asked to be transferred. And then the answer from Kevin was precise and issue resolved in 2-3 minutes (after waiting on hold for 20)
But Wait!! Read on....Here's where this gets interesting. Turns out that I WAS talking on my phone clearly for almost an hour with NO drops. Turns out the HD Voice signal is significantly better to my home, that the regular voice signal. I was not even aware that I wasn't on the NE until I had tried to dial #48 to check. I even told Kevin about this. He said the HD voice signal is stronger and operates on a different frequency, and depending on where we live, it's possible that it's getting through, whereas the regular voice signal cannot. Sort of like AM and FM radio. Where the FM is clearer, but need to be in range of signal.
So I have left the HD voice turned on, to get this an honest test. I'm also keeping my NE active, just in case.
Would love to here of any other situations where going from NE to HD voice works, whereas, regular voice without NE did not.