eXDee: Where did you buy your so-net sim? At the narita airport, Mobile Center only sold an overpriced 1gb one which they were out of stock of. They instead pushed what seems to be their own MVNO "Wi-Ho!" which was considerably more expensive. Ended up getting one as we needed data and didn't have time to mess around - which is probably what most people do.
I went there on the advice i read that they sold them there, would be curious where to look in the future at Narita.
This was nearly a month ago now, so my memory is a bit hazy. I got it from Terminal 1 (where Air NZ land). It wasn't far from the arrivals gate, turning left I think. It was one of the first places that I saw from memory. I did shop around for a short while to see what else was around, there were about 3 or 4 different places with various pocket wifi and SIM cards.