The UCM/4G works on 4G (or LTE) networks. It is not able to work in 5G -only networks, but 5G SIM cards can normally work on 4G Phones.
However, UCM/4G makes use of 3G for Voice calls - it does not support VoLTE (Voice Over LTE).
If the SIM card uses VoLTE for voice calls then Voice calls will NOT work on UCM/4G.
To fix this, disable VoLTE on the SIM Card. This is done by inserting the SIM Card into a Phone and changing the settings. On a Samsung Phone, go to Settings > Mobile Networks > VoLTE Calls, and Unselect this feature.
In the latest Samsung OS, this feature may be grayed out, ie it is automatically selected based on the Phone and SIM Card. If that is the case, an app that can show these disabled buttons is the "Samsung Band Selection" app from the Play store, https://play.google.com/store/apps/details?id=com.ray.samsungbandselection&hl=en&gl=US
Note that this is NOT from Samsung This allows the VoLTE feature to be disabled.
Also if the SIM Card is 5G, Disable "Use 5G Standalone Networks", and select Network Mode = LTE/3G/2G (auto connect).
Remove the SIM Card from the phone and insert into the UCM/4G. The UCM/4G should now be able to dial out by voice calls
Last edited on Saturday Nov 18th, 2023 07:30 am by slychiu