iPad Wi-Fi + 3G: What exactly will 'unlocked' mean for roaming consumers?

According to Engadget and a variety of souces reporting on the matter, the iPad Wi-Fi + 3G model will come completely unlocked giving consumers the ability to choose the data provider of their liking

In the US, this means an AT&T pre-paid non-contract service, for now. Hopefully, others will follow.

Meanwhile, what does this mean for other markets? Japan for example, has always strictly held to a stance of locking consumers into their devices for multi-year contracts. Will Softbank, who currently operates the iPhone, or NTT Docomo, Japan's largest provider which is rumored to be eyeing this iPad opportunity, follow the AT&T's lead and allow a pay as you go non-contract, or at least non-locking plan for the iPad?

The latest rumors in Japan, more focused on general mobile phone use and unrelated to the iPad, shockingly point to yes. Rumors are that the major Japanese carriers are considering changing the business model to include unlocked phones allowing consumers to compete for their services, rather than the phones they provide. Though one Japanese article mentioned that these companies are feeling pressure from lost business as traditional users are attracted away toward the iPhone, which currently means only Softbank.

Now back to iPad. What I'd really like to know is, as an international traveler, will I be able to buy my iPad Wi-Fi+3G in the US and use it in Japan with a 3G data plan? Or conversely, can I buy my iPad in Japan and use it with a plan from AT&T? Since I'm not really willing to be the guineapig, I guess only time will tell.

Though ultimately, in my opinion, the best option would simply be to allow tethering with the iPhone. Why pay for two plans that do roughly the same thing..