cheapest provider for ringing australia

What is the best way for phoning mobiles in Australia. I know that Viber, whats app and all those applications are good but then the person in Australia has to be on the internet too.

I see Vodafone do a top up which includes international minutes. Any other deals out there?

Tesco mobile offers calls to Australian mobiles for 12c per minute

Skype pay as you go costs 20c per minute (you use your PC/Laptop, buy Skype credit and phone the mobile no as normal).

Not sure how they compare with other providers, just two I thought of.

Edit: Just spotted monthly subscriptions on Skype that might be of interest too - 60 mins to Australian landlines/mobiles for €3.99 pm or 120 mins for €7.99 pm

Thanks gipimann will check out the Skype one. Am tied to meteor at present and they charge 15c a minute. Vodafone have a good deal with their red package but can't move so looking at other options.

I use this:
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Once you register you get a (credit type) card in the post and all you need to do is top up in your local post office with the card. I use it with my land line to make calls to Australia and Europe and you would be surprised how long a 10 or 20 euro top up lasts.