a better (and not too explicit) set of regular expressions for japanese phone numbers based on ministry of internal affairs' spec (総務省). http://www.soumu.go.jp/main_sosiki/joho_tsusin/top/tel_number/q_and_a-2001aug.html
^0(\d{1}-?\d{4}|\d{2}-?\d{3}|\d{3}-?\d{2}|\d{4}-?\d{1})-?\d{4}$
^0[789]0-?\d{4}-?\d{4}$
^050-?\d{4}-?\d{4}$