This I write so others do not need to spend 2 hours troubleshooting as I did 
Happy FP4 owner since over 2 years here. My old provider was bought by another one, so I received a new SIM. After SIM change my FP4 had no data connection anymore. The solution was to manually set the APN address, up to then empty, to that of the new provider.
The good: APN issues are often named in these forums, and this led me to the solution. Thanks!
The bad: I spoke twice with the provider, with two different persons, and no one of them suggested me to have a look at the APN issue. No surprises here. People in customer service rarely know more than saying “restart the unit”. Also, the APN address was found in some obscure site listing APN address in my country, not on the official provider webpage. No surprises here either.
The ugly: I tested the new SIM in both an 8 year old Huawei and a 4 year old Samsung, and both worked right away without any need to do anything other than to set the SIM inside! So why not FP4? I am moderately technically skilled and it took unnecessarily long time for me anyway to solve this. What if this happens to an elderly or less technically curious person? Please Fairphone people, here there are some sharp edges to smooth out!
Keep up the good work!
hello and welcome to the community forum
Thank you for sharing your experience. I can imagine how frustrating it is when things (we rely on) stop working unexplicably
it is also unfortunate that customer service of many providers is not that helpful
we recently had a similar discussion on the forum where APN turned out to be the key which led me to double checking the FP support pages
perhaps it is not the easiest to find but there is a troubleshooting page mentioning APN
https://support.fairphone.com/hc/en-us/articles/9498003764113-How-to-fix-mobile-data-and-network-connection-issues-on-your-Fairphone
and if you go to self-repair portal, this is the second step suggested (at least for my FP5)
Thank you, I missed to mention that I have also seen that page.
What I meant by “sharp edge” was the fact that two units (one of them 8 yrs old!) by two other different manufacturers did not need an APN reset or anything, while the FP4 did. Perhaps something at the hardware level?
This is in no way a harsh criticism. I hope it is received as of the constructive type, as intended. I like Fairphone, I recommend them to everyone, and will continue doing so.
Welcome @dhdeangelis! It would be good, for the future, to know which provider the issue is with. One of the easiest clues that something might need updating is when in the carrier settings version (for the FP6) does not give the MCC and MNC combination corresponding to your network. Also, unfortunately, very often when the provider is bought, even though the carrier settings ARE there, the APN settings are no longer for the correct operator.
Unfortunately most providers now seem to operate on the assumption that their APN settings will always be automatically recognized by the device, but in some cases this is just unrealistic.
(Edit: This is more a provider than a hardware issue - APN settings are programmed into Android’s carrier settings, otherwise they go a default settings that allows “most likely”. One of the more frustrating component, which luckily does not seem to apply to Fairphone so far is that even though your provider HAS VoLTE and VoWIFI, Android’s carrier settings don’t reflect that and there’s no way to bypass that lock out until an update is provided to Google)
Thank you @wallacewells for you reply.
The old provider is Bredband2 and the new one is Telia, both in Sweden. APN details are:
Ah! It looks indeed like the Fairphone 4 should have supported Telia automatically. Don’t try it now, but in the top right corner under the APN settings it should say something like “Reset to default”, even if that is otherwise completely empty and that would have probably triggered the correct APN settings after the SIM swap But since it is all sorted now, enjoy!!
