Walk into a Telstra Shop.
"Hi, I'm currently a customer with 3 and I'm sick of their shitty service. I want to switch carrier to you guys but keep my current number, what can you do for me?"
Watch them fall over themselves trying to get you to switch.
I did this when the iPhone 4 came out. I had been a business customer with Optus for 7 years and they told me it would be a two month wait for the iPhone as my contract had 6 months to go at that point. I walked into Telstra and they had a phone in my hand, doubled the data allowance for the plan at no cost, paid my early exit fee from Optus and paid the transfer fee for the number and had it all done in less than 30 minutes. Two month waiting because of contract reasons is not how you treat a customer who has been with you for 7 years. My entire family pulled their contracts and went to Telstra as well for more or less the same reasons with similar results.