I was speaking with a friend today who was thinking of buying an iPhone from Singapore and purchasing just the SIM card with dataplan from Softbank here in Japan. It makes sense because the Japanese iPhone can only be used in Japan while the Singapore iPhone can be used all over the world just by purchasing a SIM card. I thought it was a good idea until we spoke to a new friend who is doing just that. Since the SIM card size is different, she even bought a SIM card cutter to get it to the size for her iPhone.
She realised that somehow, the SIM card doesn’t charge as if it’s a Japanese phone and when she went online, she was charged roaming fees. She ended up paying over ￥30,000 for her phone charges. So if you intend to do the Singapore iPhone Japanese SIM card thing, don’t. Unless you do not intend to use the data.