Thanks for the link. Unfortunately, with the disappearance of Riiing into UM the au site is no longer able to provide recharge services. Their email to me follows:
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Thank you for your enquiry.
As a result of recent changes in the commercial arrangements with United Mobile, the operator and supplier of the RiiiNG service, we are unable to provide the recharge service any more.
To recharge your RiiiNG SIM card, please go directly to the United Mobile recharge page on the United Mobile web site, which is at
http://www.united-mobile.com/UMShop03/recharge.asp where you can pay with your credit card online.
If you have any other questions, please do not hesitate to contact us again.
Regards,
Customer Service
Convercom Pty Ltd
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Looks like the minimum now is ?25.