Recommendations for data and voice pre-paid SIM card for Perth Australia

[behyx]

Hi all!

I frequent Melbourne and I have an Optus pre-paid SIM card for my usage there.

However when I was in Perth, I can't seem to find Optus network, thus I couldn't top up my SIM card.

I'm heading to Perth again in 2 weeks time, thus what is the best affordable telco for data and voice pre-paid SIM?

Also I will require it to be able to tether data to my iPad and other iPhone too.

Thanks!