Hello everyone,
I’m trying to use a second SIM card in my Jolla C2, but I’ve run into a problem: it seems that only one SIM slot can use a 4G connection at a time. The other SIM is limited to 3G/UMTS. I’ve verified that both SIM slots support 4G and VoLTE individually, but as soon as I insert two SIM cards, only one of them can access 4G and VoLTE.
Now, you might say that having 4G on both slots isn’t strictly necessary. However, the real issue is that in Switzerland, 3G networks are being phased out. For example, Sunrise now only supports 4G, while Swisscom still supports 3G until the end of 2025.
My primary provider is Yallo (Switzerland, which uses Sunrise). When using only the Yallo SIM, everything works fine, including VoLTE. But when I insert a second SIM from Sunrise, this second SIM fails to connect - because there’s no 3G fallback available. To test further, I replaced the Sunrise SIM with a Swisscom one, and as expected, it connected via 3G/UMTS, while the Yallo SIM continued to use 4G/LTE/VoLTE.
Both SIM cards are set to use 4G in the settings, and both are 4G/VoLTE capable. I even tried with other Sunrise and Swisscom SIMs, but the behavior remains the same.
I’m not sure whether this is a hardware limitation (I had a Huawei P8 Lite 2017 with a similar issue) or a software one.
Can anyone shed some light on this?
Thanks in advance!
Device: Jolla C2, Sailfish OS 5.0.0.70 (Tampella)