For those who use Mifi's a hint - if from the US

Get a Google Voice acct and forward your phone to Google Voice when you don't expect incoming calls. Then install Google Voice app.

Instant ability now to "screen" calls; you get alerts via Google voice (thru data) on those leaving a message - you can then use Skype or similar to return calls if on a good Mifi+good network.

This lets you avoid call charges but remember also if you get an incoming call and you reject it - YOU STILL get billed a 1 min charge for the divert back to voicemail.

If you really want to receive calls on the US number you have get a Skype number and just forward your US number to that.

I don't do the Skype forwarding - the last thing I want is people in the US ringing me 10AM US time which is 2AM Japan time! I just leave my phone on forwarding to Google Voice