Optus, one of three Australian iPhone carriers, has revealed its plans and pricing for the iPhone 3G. Unlike most other carriers, Optus is offering the iPhone 3G to subscribers on a monthly payment basis, in lieu of taking one large upfront payment for the handset. The company will offer the iPhone 3G with two different lines of contract service plans. The company’s ‘yes’ Cap Plans offer a set amount of data, a credit amount used…