I'm on docomo and I only have a SIM from them, I brought my own iPhone from abroad. When I turned my iPhone in to Bic Camera to have the display swapped, I could just swap my SIM into a spare old phone quickly and it worked seamlessly.
Oh that's good, I went into one of their branches and they told me it wasn't possible and I'd have to buy a phone from them. Probably just pushy salespeople trying to meet quota.
I'm on docomo and I only have a SIM from them, I brought my own iPhone from abroad. When I turned my iPhone in to Bic Camera to have the display swapped, I could just swap my SIM into a spare old phone quickly and it worked seamlessly.