Amaysim's pay-as-you-go call rates were already fairly low at 15 cents per minute with no flagfall, but now they're a little cheaper. The standard per-minute rate for all Amaysim As You Go customers has dropped to 12 cents per minute from today, and some international call rates have also fallen.
Other rates (for SMS and data) haven't changed. The international call rate cuts impact 30 countries (and also apply to postpaid customers); you can see a full list here. If you're after a prepaid plan and you're happy with the Optus network, it's worth considering.