Originally Posted by
CheckInPeach
If a SIM is supporting several networks in one country, from my understanding it's not the phone choosing the best. The system is not that sophisticated. The SIM contains a list of supported networks in each country, the list has a priority indicator, so it's the most preferred it is connecting to first.
I use two SIMs of two different carriers (not MVNO). I frequently do speed checks when I'm roaming, even when both SIMs connect to the same network. The speed varies quite often which IMHO is because of capacity issues in the local network. When roaming with legacy carriers, your exit point is in the country of the carrier.
I now rarely manually choose a network. I carry 2 phones travelling. I used to manually change networks a lot, especially when Google FI was rolling out. All connections are much improved in the past 10 years. I also do speed checks if something is a little off. But most of the time, no switching necessary. I do still carry
the "secret" codes, if i need them. Android too.
All iPhone Secret Codes – Tested and Working (October 2025) - TechWiser