I bought an 8830 Global Edition from Verizon 18 months ago, and have head nothing but headaches with the global part of that name. Most recently I traveled to Japan and found I have no phone or email service at all. This was after contacting global customer service before departure (when I as assured it would work) and a 20 minute landline conversation with gobal tech support (which decided it was an equipment issue).
Come to find out that in BB and Verizon speak, Global basically means Canada and some parts of Mexico. Would one not expect a phone advertised as being "global" to work in what is far from a third-world country?
Japan has odd frequencies compared to the rest of the world - are you sure that the 8830 has the correct radio? IIRC the 8830 is a dual-band device, not quad, so there may be no service in Japan for you.
Japan has areas of CDMA mostly for voice. If you want data, you would need GSM. There are still many areas that still ue their old PDC technology. They are expanding CDMA all the time though