I have two mobile phone numbers in Japan, one is DOCOMO’s Ahamo and the another one is b-mobile. As mentioned by the telecommunications company, both b-mobile and docomo need to install a profile on the iPhone when first using it, but only b-mobile's profile will affect the APN settings.
One day, when I switched back to the Hong Kong CSL account number, Ahamo suddenly could no longer connect to the telecom provider.