However, most Japanese phones won't get 3G service because T-Mobile uses UTMS band IV (AWS), which splits uplink and downlink between bands roughly at 1700 and 2100 MHz. In Japan, Docomo and Softbank use 2100 for both, while Emobile uses only 1700. The only other US carrier that would potentially work with Japanese phones is AT&T, but they use 1900 MHz. (Nicholas thought his Galaxy S2 supported this frequency, but he is in the US right now, languishing on 2.5G EDGE.)
To be fair, Japan's urban 3G coverage is excellent. In contrast, while in a major US city, my connection often fell back to EDGE, even though my phone is the T-Mobile version.
Cost for 10 days of service with T-Mobile
There are, of course, some caveats. First off, the SIM card must be purchased for $10, though this is half of what Docomo charges (¥2,100). The SIM card expires after 90 days of inactivity and can't be subsequently refilled. Refills are purchased in $10 increments, which is why I only bought 10 days of service (for $30).
In computing, an asterisk * is a wildcard that may stand for any character. To cell phone companies, it is a mathematical operator that changes the sign of the term it follows. For example, plus one (+1) becomes minus one (-1). Night becomes day. 4G becomes 3G, and unlimited becomes limited. This brings me to my only gripe with T-Mobile; their advertising is a disingenuous.
How do they get away with calling a 3G network 4G? There is a strict definition of 4G. Docomo's Xi LTE network is probably the world's fastest, but Docomo doesn't even call it 4G. Because it's not, not until it reaches a theoretical downlink of 100 Mbps. So Docomo calls is 3.9G.
This "4G" term is also used in the fine print on the unlimited* data plans, which is wrong in more ways than one.
First 5GB at up to 4G speedA plan really isn't unlimited if data is throttled after exceeding a cap, and this statement makes it seem like you'll be reduced from 4G to 3G speed. In reality, 4G speeds don't exist, and after the cap, speeds are reduced to 2.5G EDGE speeds.
But these are really minor gripes, and I guess in the US, this type of advertising in to be expected. With every company doing, those who don't would be at a major disadvantage.