Be kind to a first poster - not sure if this belongs in the deals section.
The link pretty much says it all, but as a quick summary, from Fri 12 Sep (in-stores) or from Sat 13 Sep (online), Virgin is offering a Bonus 2GB on their 24 month contract plans for customers who swap from a non-Optus network to an Optus network, or for current Virgin customers who wish to recontract. (N.B. if you're currently an Optus customer, it's easy to buy a $2 Vodafone Sim and port your number out, and port back. It's actually often safer in terms of porting, as sometimes porting numbers on the same network goes wrong).
Data is billed per kilobyte (kb) including uploads and downloads (not per mb like with Vaya and other 'too good to be true' deals). Virgin uses the Optus 4G network. Obviously no where near as good as Telstra with coverage and speeds, but at least it's affordable. You also get benefits from rollover credit (per month) but NOT data. (Also includes free Virgin to Virgin calls and texts and credit includes international calls and texts).
Below is a little thought experiment, which, depending on how Virgin, and other providers price their handsets, may or may not turn out to hold true.
I know there aren't an overwhelming number of Apple fans on OzBargain, but given this deal lasts for a while, this might be one of the best ways to go about an iPhone 6 (/Plus). As someone who has devoutly bought outright phones and paid for cheap plans (currently on Virgin $20/month w/1.2GB data & $200 credit), with plans becoming increasingly more expensive, paying outright + plan is becoming as expensive as buying phones on contracts, however contract phones tend to be much more generous with credit and data (often unlimited calls and texts in Aus). With a bonus 2GB data, most should be pretty set.
For example, a 32GB iPhone 5s (which should be equivalent (or cheaper than) to a 64GB iPhone 6 as both are the second storage option *) currently costs $60/month on Virgin, ($30 phone, $30 plan) over 24 months = $1440. With $300 included data, and a meagre 300mb of data, this plan is suddenly much more attractive with 2.3GB of data. Furthermore, it's easy to opt-out of Virgin at any time over the 24 months, and only pay remaining handset costs ($720 including what you've already paid). They're also kind enough to unlock your phone for you. If you don't want to tell them you're changing to another provider, just say you're going overseas.
The iPhone 6 64GB retails on the Apple store for $999. If you're paying $20 a month for a plan over 24 months, $999 + (20 * 24) = $1479. (ie already costs more and I doubt you'll get as good a plan for $20).
You may be concerned about the low credit (only $300) but where most use internet messaging services (iMessage, Facebook Messenger, WhatsApp,Viber,Skype…) and with calling from WiFi coming to Australia, hopefully by 2015, I'd definitely be more concerned with Data allowances over credit.
*iPhone 5S storage options: 16GB, 32GB, 64GB
iPhone 6 (/Plus) storage options: 16GB, 64GB, 128GB
I believe second tier storage options will be equivalent in cost at release (with the 6 Plus model costing ~$100 more)