I have an Xperia 10 III with Lebara (Australia) SIM in Slot 1 and an AIS (Thailand) SIM in slot 2.
Data from the Lebara SIM works OK.
I have an iPhone which I also use for my European SIM (no roaming) and in this case, I left my iPhone connected via the SFOS hotspot to the Lebara SIM. Data was consumed at a constant rate until ca 5GB were gone (Edit: Total amount according to data counters indicator) I have no idea why, I didn’t download or upload movies or anything even close to that amount of data.
The flat top graph suggests something strange but impossible to determine what caused it. I was asleep for half of the time and no data should have been used. iOS wasn’t updated during the night.
Any clues what could have eaten my data?
Edit: I should add that in 4.4.0.58 and .72 various combinations of turning on/off internet sharing, wifi and data cause loops from which the only escape is rebooting the machine. This functionality is terminally broken. Turning on/off data, wifi and sharing is a requirement in high cost data areas