Hi @Bryn P 

I’m sorry to hear this, unfortunately my best advise would be to purchase a device that is present on the supported devices list.

Tom

Hi,

I would recommend you make a call, to voicemail or to anyone, ensure that VoLTE is properly working on your Unihertz Jelly 2E, if you stay on 4G during the call, you should be fine after the 3G sunset, if it drops down to 3G, I would make sure VoLTE is enabled, if that doesn’t work, follow @Tom ‘s advice to buy a new phone from  the supported device list. The phone doesn’t have to be necessarily from the iD shop. Just ensure it isn’t carrier locked or anything. And ensure that VoLTE is supported.

I waited until after the deadline and found my phone still worked on the 4g network. Luckily I did not purchase another phone as recommended by Tom, particularly as I had only owned the current one for about a year and do not use it much. 

I have to disagree with @Tom at this point.  It not may be down to an ‘unsupported phone’!
I have had experience with having a 4G VoLTE enabled phone which was ‘supported’ by a network and yet it still didn’t work when connected! Even ‘if’ it isn’t supported by a provider it may still have the capability to work!
Everyone knows that phones should be ‘unlocked’ so that all network SIMs work when changed over in a device. YET, not many realise that the Firmware on a device is also constrained by those same networks!
For example:-
I was gifted a Samsung Galaxy J4+ from my sister.
Originally I was with SMARTY but they didn’t ‘support’ this device for VoLTE so I eventually moved to iD who did ‘support’ it.
Once SMARTY (Three 3) had switched off their 3G network I was unable to make/receive calls for many weeks and so I moved over to iD (who ‘supported’ my device) and yet I was still in the same situation where I couldn’t make or receive calls.
After >30hrs of research, I found out that the Firmware contained on my device was controlled by Vodafone (the original network/seller of the phone) and so unless I was ‘connected/subscribed’ to their network I wouldn’t get the software updates to ensure the phone was ‘up to date’ and had all the options available to ensure it worked.
This is the same for ALL phones sold by a network! 
I researched how to determine the Software Information of my SG J4+ and I found it was - SAOMC_SM415FN_OVF_VOD_PP_001 - 40009a7d VOD/VOD/VOD.
VOD is the designated code for Vodafone! Therefore Vodafone controls the ability of my device to work through Software updates.
The ONLY way to circumvent this is to ‘Flash’ your device to ‘Unbranded’ Firmware so that it is updated from the manufacturer rather than a mobile network.
I did this and now my phone (SG J4+) has so many more options, including VoLTE and WiFi Calling, that it didn’t have before.
I can’t say that IF I had ‘Flashed’ my phone whilst still with SMARTY that it would have worked BUT until a device is uncontrolled by a networks Firmware I won’t know!