After looking at the different plans etc, I decided I could get basically an iPhone 60 plan on XT Prepay so have purchased an iPhone 3GS outright (when it arrives). 

Here's how....

Load up $60.00 credit on your prepay - XT then gives you a $20.00 bonus credit. $80.00 total.

Pick a Text 150 extra for $6.00 and a 240MB data plan for $18.00. You have $56.00 left for calls. 

At the standard call rate of $0.89 cents a minute, you have enough left for 62 minutes. And the best thing is, (apart from not being locked into a 24 month contract), if you don't use those minutes, it will roll over to the next month.... 

You also have the benefit of using a lower data plan (120mb for $12.00) giving you more talk time if you want. 

Even compared to the equivalent $40.00 iPhone plan, you would still get more texts and talktime if you topped up $40.00 on XT and got the extra $12.00 bonus credit. 

Just have to cancel my current VF plan now...