I'm not suprised it's number one now either.
I don't think it caught on until they started the iPhone for Everyone campaign. (0 Yen for the 8GB) Oh and you need to have established credit in Japan. I had to pay mine up front and then they refund a little every month.
Living in Japan and walking around with my iPhone I find that many Japanese I run into want to check out my iPhone. They'll play with it for a while and tell me they want one. Usually they're waiting to get out of the current contract.
A couple other things that slowed the adoption:
1) Softbank is not known as the best provider. People complain about their customer service quite often. The coverage isn't exactly the best either. It is more the new kid on the block here.
2) The way the phone charges work, your cell phone plan only counts towards calling people on the same network. With Softbank not having the largest market share this keeps a lot of Japanese loyal to their provider because that's what their friends have. If you call AU or a land line, you incur charges over and above your plan. At least you don't pay usually for incoming calls. But if you want to call your friends who don't have an iPhone, you're going to pay so keep it brief.
3) Before they introduced the packet rate discount your bill could be well over $100. That's close to the base rate I had with my iPhone in the states but the Japanese are used to paying a lot less.
4) Emoji! Definitely it lacking originally was a big drawback. See the above charges for using your actual phone and you'll see why they spend a lot of time texting and Emoji are a big part of that.
Now on the plus side:
1) The majority of Japanese do not have home computers. This country is a deadzone for Wi-fi and most of their Internet browsing and other activities is done on their phones. My wife has one of the fancy phones here with TV and all and the web browser sucks compared with an iPhone and Safari. Many of them are looking forward to being able to surf the web with something decent.
2)Games. Many hours on the train everyone is glued to their phones or PSP's playing away. If you combine the gaming of the PSP with Internet and phone the marriage is made for the commutes.
3)As mentioned above, the GS came out just as the marketing push really started taking hold.
Hehe... I like the comment about not caring about the voice control. The Japanese cover their mouths when they speak in public so as not to disturb others around them. I really don't see them embracing voice commands...
btw... just in case anyone thinks about bringing a foreign iPhone over, Softbank in June started cracking down on "foreign" iPhones on their network. Even though you buy the packet discount and all the iPhone packages, Softbank will charge you per packet. I unlocked my old AT&T iPhone 3G for my wife to use because she wasn't happy with the "gadget filled" phone she originally got from Softbank. Well it worked fine for the first couple months, then out of the blue we got a bill for $1600 and another for $400. This has happened to a number of other people as well. They eventually refunded much of it with the promise that we wouldn't do it again.