Well, someone helped me resolve this (no not Tmo, but it wasn't a Tmo issue). Seems the Nokia 6 no longer switches to HSPA+ mode in order to process the short code (USSD) which it needs to do, the workaround is to temporarily toggle the Nokia 6 to 3G, once this is done, the short codes work. I can then place it back onto 4G (LTE).
It used to work, so I am wondering if a recent Nokia update changed this. Not a big deal, I just have to toggle to 3G use the short code, then go back to 4G, a few seconds.
This person stated he had an issue with his LG, and found a setting to allow USSD over IMS in the hidden menu to resolve this so he doesn't have to toggle back and forth. I did not see this option in the hidden menu, so the 6 may not support it.
09-30-2017 08:31 PM