Surveys ahead of the upcoming launch of number portability in Japan show that roughly 25% of Vodafone Japan customers are planning on changing operator, with around 19% of Docomo's customers thinking of switching, and only 8% of KDDI's customers unhappy enough with the service to consider changing.

Whilst the overall number of people considering changing operator is down from the last survey, it is likely that the cost and problems with switching providers, which are becoming clearer as the service launch date approaches, are likely having an impact on the decision to switch and retain an old mobile number.

It's also not surprising that KDDI came top of the survey of preferred destination, given the low number of people thinking of leaving that carrier for another.