I have used a service called VoipCheap for a few years now and have a free period each time I top up my credits. Calls from Japan to a UK land line are just 1p per minute.
The quality is usually pretty good with the occasional lock up, requiring a redial.
I've never used Skype for paid calls since it was more expensive when I started with this service.
But when I call my online banking where I think the call center is based in India, all the redirection can make it a bit difficult to comprehend what the operator is saying at times. And I have to be very clear with my instructions to them where they sometimes don't get what I have said.
But this may be the same with Skype, I don't know.