Wanted to follow up to a now autoclosed thread Unknown caller unless volte and vowifi disabled - #4
In the previous episode…
I was using the Polish branch of the carrier “Mobile Vikings”, which is a MVNO of the Play carrier. VoLTE and Vo-WiFi didn’t work.
Switching to a supported carrier
I did not realize that Fairphone has a list of supported carriers:
https://support.fairphone.com/hc/en-us/articles/9779766652689-Set-up-4G-and-Wi-Fi-Calling#compatibility
The only FP5 carrier listed for Poland is “Telekom”, which is short-hand for “Deutsche Telekom”, which is simply T-Mobile.
Because as shown in the previous thread, VoLTE and VoWi-Fi didn’t work (every call I got was “unknown caller”), I simply switched my carrier from Mobile Vikings to T-Mobile (“Telekom”). Because I’m using a pre-paid plan, I needed to text “TAK” to the number 80535 to enable IMS (the stuff that makes VoLTE and VoWiFi work).
Please note that the equivalent device support list on T-Mobile’s side doesn’t list Fairphone 5 as a supported device - VoLTE i VoWiFi – wybierz najlepszą jakość połączeń| T-Mobile - even though FP5 lists T-Mobile as supported. Have fun with T-Mobile support calls if you ever need to)
Detailed diagnostics to make sure it’s now working
You can view detailed diagnostics about IMS, VoLTE and VoWi-Fi status by dialing the short code *#*#4636#*#*" in your phone app, going to “Phone information” (first option). Then, wait 2s for the three vertical dots icon to appear in the top right. Press it, and select “IMS Diagnostics”.
The first line should read “IMS Registration: Registered”. If that’s not the case, it means you need to enable IMS with your carrier (in the case of T-Mobile prepaid, text 80535 as mentioned previously). If this line doeen’t say " Registered", the below two lines about VoLTE and VoWifi eill always say unavailable. IMS is a prerequisite for VoLTE and VoWiFi to work. Being unregistered with IMS is likely a carrier issue rhather a Fairphone issue.
If you are disconnected from Wi-Fi, but connected on mobile data, “Voice over LTE” should read “Available” and “Voice over WiFi” should say “unavailable”.
If you are connected to Wi-Fi, “Voice over LTE” should be “Unavailable” and “Voice over WiFi” should read “Available”.
Calling people
When calling people though the Google “Phone” app while connected to Wi-Fi, I can see a Wi-Fi icon appearing next to the call duration, so I’m assuming VoWi-Fi is working fine.
On stock ROMs (I’m on rooted LineageOS with MindTheGapps, so doesn’t apply to me), you can see a “HD+” square icon next to the call duration in the Google Phone app when calling over VoLTE. I’m on a custom ROM so I probably could never see that icon. But I assume that it’s working since IMS is saying VoLTE is available.
Note that adding a “ims” APN wasn’t necessary, as some Pixel volte GitHub repo issues say. Adding that made my calls immediately drop.
RCS side note
Play’s (my previous carrier) implementation of RCS - the “fancy SMS” - unrelated to VoLTE or VoWifi - only works on Samsung and Huawei phones so if you want RCS to work, it may be a good idea to switch away from them too (not necessarily to T-Mobile). It also didn’t work on a stock ROM Xiaomi Redmi Note 8T, so I assume it’s not a Fairphone issue.
For more information in Polish, see here:
On T-Mobile RCS works for me on a rooted LOS with mindthegapps with this setup:
https://xdaforums.com/t/rcs-and-root-how-to-get-rcs-working-and-discussion.4678661/post-89743091
For more information about on which Polish carriers RCS works, see:
Extra references
There’s also this very nice database showing where VoLTE and VoWi-Fi works on which phone in what Polish network (there’s an entry for FP4): https://wificalling-volte.pl/