How can I use WhatsApp on a Japanese data plan phone?

A

AC Question

I visit Japan frequently, and have a Japanese SIM card that I use in an Android phone when there.

Due to Japanese legal restrictions, my SIM card is for data only. Thus, in a standard work-around for foreigners, I get voice by running VoIP software (in my case, something called SmartTALK). This gives me a fixed Japanese VoIP mobile phone number (050…).

I have WhatsApp installed on this phone, and would like to use it as SmartTALK does not have messaging options. However, when I enter my 050 number, I am told that it is not recognised.

How can I use WhatsApp with my Japanese phone? Is there another messaging package that I should be using which would be compatible with SmartTALK?

Thank you