FeliCa and USIM

I always wondered how the phone, which contains the FeliCa chip, and the USIM card, which contains your identity. E.g., when you move a USIM card from phone A to B, where’s your money stored, e.g. your balance with edy which uses FeliCa?

Today I got the answer.

The FeliCa chip gets ‘branded’ with a USIM card. Once done, the FeliCa chip won’t talk to any other USIM card. So if you want to use a phone with another USIM card, you have to erase the contents of the FeliCa chip. The phone with your new USIM card cannot do this though as it cannot talk to the FeliCa chip. In my case I had to go to a docomo shop and they erased it via a FeliCa reader/writer.

Afterward using FeliCa is no problem. Before that I always got an error about “there’s stuff there, erase first” without telling me that as much as I try, this is not something I can do.