@domo141 @J-One This is a general Xperia 10 III issue, also present on Android (actually all versions I’ve tried, from 11 to 13), not related to SFOS. I have no idea when it appeared and what caused it, but if a single SIM card is used (no matter in which slot) then the phone has MAJOR difficulties to register on 2G network. If “2G only” (GSM only) mode is selected, it sometimes takes many minutes to register (and often it is not possible at all), and even if it eventually manages to register then it drops network again after every communication (phone call, SMS, etc) and again it takes a lot of time to re-register to 2G network. It doesn’t depend on network signal level, it happens even with 100% signal strength. It only affects GSM (2G / 2.5G) connectivity, whereas 3G and 4G work perfectly fine.
I’ve found a simple (but really bizarre) workaround: you need to insert TWO SIM CARDS, in both slots (which unfortunately prevents the use of a memory card). The other SIM card can even be old and no longer active (or the cheapest prepaid card, not activated and not charged with any credit), and then you can even disable it in settings, but it just has to be placed in the slot. As soon as the second SIM card is inserted, “2G only” mode starts working (for either or both cards) and you get instant connectivity to the GSM (2G / 2.5G) network.
Please try if it works for you and kindly report it here if it does.
This is actually the most bizarre thing I’ve ever encountered with a mobile phone. As I said, I have no idea what’s causing it. It can’t be a hardware issue if it only affects 2G connectivity while 3G works fine. It can’t be a SIM slot / reader issue, because it doesn’t matter which card is in which slot. And it can’t be antenna issue if as soon as both SIM cards are inserted 2G network starts working perfectly fine for both slots. I’ve tested it with three different SIM cards from three different Polish mobile networks (T-Mobile, Plus, Orange) and all of them are equally affected. So it is not a network or SIM card problem, either. All those cards work perfectly fine in “2G only” mode on my XA2 Ultra. It looks to me like a software bug, maybe in 10 III modem firmware.
Can anyone else please also test it and report if his Xperia 10 III connects to GSM (2G or 2.5G) network in “2G only” mode with just one SIM card inserted?