Thanks to mjwills who posted this comment on OzBargain, which leads me to this thread on Whirlpool forum, where a trick is discussed to use Optus Prepaid’s call diversion functionality to make mobile calls to any phone at 10 cents per minute. I am a bit of a late comer on this, as the trick was posted a year and half ago. However it seems to be still working.

If I have read it correctly, the trick basically goes like this:

1. Buy an Optus prepaid mobile SIM pack (available pretty much everywhere). Get the one with maximum free time with other Optus prepaid.
2. Activate the SIM, and get a new number, for example “0411 111111”. You will also get 300 free minutes to other Optus prepaid mobile phones.
3. Now to use your new SIM to call another number, for example “0422 222222”, you need to set up your own phone to automatically divert to that number. Dial **21*0422222222# to set up this diversion.
4. Call yourself! Dial 0411111111 on your phone.
5. Optus will figure out that the number you are calling is actually busy, which then triggers the call diversion to the number you actually intended to call. Since you are calling an Optus prepaid number (i.e. your own number), which is free (but will use up your My Time minutes). However, call diversion is charged at 5 cents / 30 second block, making it effectively the only cost on the call.
6. Remember to UNdivert the phone after you have finished. Dial ##21#.

It is a bit troublesome to set up if you need to do lots of calls, but I think it will bring quite a big saving for those who used to spend a lot on phone calls. The minimum recharge on Optus prepaid mobile is $30 which lasts 60 days. So it might be worthwhile to try out if you spend more than $15 a month on mobile calls.

Another suggestion is to cancel the diversion as soon as the phone is ringing. It will be very confusing if someone else calls you while you are on a call, and he/she gets diverted to the voice mail of the person you are currently calling!

I am more surprised that Optus has not yet cracked down on using this trick to make cheap phone calls. Or maybe I should not have written this post as this diversion trick is now more publicised, calling Optus to respond…