Here are the specifics of my use case.
I both live and work on both sides of the US-Canadian border.
I have two lines of service: T-Mobile US and Freedom Mobile Canada.
I have been successfully using my Fairphone 4 on FM Canada with the exception that FM was unable to provision the handset for both VoLTE and VoWifi.
This line of service is provisioned with a nanoSIM.
The next step was to provision the Fairphone 4 with an eSIM from T-Mobile.
I just spent most of today attempting to do so without success.
I first attempted to scan a QR code from T-Mobile from the network setup screen on the FP4 but the FP4 rejected the scan.
According the the error message on the FP4 as well as the T-Mobile service rep is to manually provision the eSIM on the T-Mobile network using the FP4 EID. Before doing so, the Tmo rep and I thought it best if I first moved my T-Mobile nanoSIM card into the FP4 since the FP4 had never been provisioned with a Tmo nanoSIM.
After installing the Tmo nanoSIM into the FP4, the Tmo data network provisioned the data settings. However, the Tmo service could not successfully provision VoLTE or VoWifi on the FP4. The Tmo rep attempted to provision these features manually without success. Even if the Tmo rep can provision the EID of this handset on the network side, it is unclear to me how to deploy this eSIM on the FP4 manually.
The US location where attempting to do this still has a 3G UMTS carrier and could successfully complete a voice call by dropping down from a 5G or 4G carrier to a 3G connection.
But the biggest surprise of the day is that incoming audio is OK but outgoing audio is not present. No one on the remote end can hear any audio. I called the handset from a different cellphone. Again, on the FP4 incoming audio could be heard but the outbound audio was silent.
Finally, the last problem I experience with this handset is with the USB/C to 3.5mm audio adapter for a wired headset. This, too, failed. I am unable to hear audio with a wired headset.
The disappointments with this handset are growing and beginning to regret buying it.
My last handsets were never sold by my service providers and not directly supported yet all of these features provisioned without a problem.
As for the headset audio problem it appears this product was not completely tested before shipping. I presume a bluetooth headset will work OK.