I am convinced that TPG has a much cheaper mobile phone plan than Optus (and Telstra too, for that matter). On TPG's $19.99 plan, you will get $300 worth of calls. In comparison, Optus charges $49 for $330 worth of calls. Or, if you choose Optus' $19 plan, you'll get just $50 worth of calls.
That is not all. Consider also:
1. Optus charges 80c per min plus 35c per flagfall. TPG charges in 30sec blocks at 40c per min and 35c per flagfall. If you call for less than 30 sec, Optus takes from you $1.15 while TPG takes from you $0.75.
2. If you are on TPG broadband service, you just pay $15 to get the $19.99 plan. Compare that to Optus' $49 for more or less the same amount of calls!
3. In TPG mobile, you can download data (i.e web, email) at 5c per 10kb, which will be counted towards the $300 worth of calls. In Optus, you will have to sign up separately for this service and pay over and above the cap value.
4. TPG has no contract. You can terminate any time. Furthermore, in TPG you can check your usage call-by-call online, anytime. In comparison, Optus provides you a convoluted bill at the end of each month which is extremely difficult to interpret. I often find dubious charges in Optus bills that are difficult to comprehend.
Forget about "free phone" offers from Optus. You can work out for yourself that it is not free. If you are interested to change over to TPG and start saving on you mobile bills, here's a tip: you can use any Optus-locked or Virgin-locked phone on TPG Mobile without having to unlock the phone. Oh by the way, you cannot use Blackberry on TPG Mobile. I was told by TPG that you cannot use iPhone, but on the internet forums I found that it can be done. More research required on iPhone.