Huh? The standard Japanese keyboard layout is Hiragana-based, and every touchscreen Japanese keyboard I've used defaults to 9key kana input. Do people really normally use the romanji IME instead?
Yes. Despite the fact that kana are printed on the keys, pretty much no Japanese person who is not very elderly uses kana input. They use the romaji (no N) input instead, and that's the default setting for keyboards on Japanese PCs.
You are right that the ten-key method is more common on cell phones (and older feature phones had kana assigned to number keys), although romaji input is also available.
