Simply download the telstra treats app, and a free chatime voucher will be shown on your device to be picked up at a chatime near you. I tried it this morning and it seemed to work fine.
iOS: https://itunes.apple.com/au/app/telstra-treats/id874794346?m…
Android: https://play.google.com/store/apps/details?id=com.telstra.la…
Edit: It appears some users are not getting the purported Chatime offer. I can only assume that this may be because you are not within the radius of a Chatime store; my Chatime store was 1.9km away from where i was at the time, so hopefully that helps. I'm not too sure otherwise :( Sorry if you weren't able to get it!
Edit 2: Feel free to post up the Chatime locations that have been successful and i'll post it up here. As the comments suggest, it is likely that not all Chatime stores are participating, I'm not too sure about this:
-Midcity Melbourne
-Doncaster
-Rundle Mall
-Rhodes Shopping Centre
-QVB Sydney
-Burwood Sydney
-Central Park NSW
-Eastwood NSW
Not Facetime alternative.