Step 1 - Your Current Contract
If you're currently on contract with Optus and you move to Telstra, you will have to pay Optus something - because Optus let you use that glorious iPhone for free/very cheap the past few months. Remember, that's a $1000 phone that they subsidised on the basis you'd hang around for a full 24 months. You broke that agreement and they want their money back. The shorter period of time you have left on your contract, the less you need to pay them. How much you need to pay exactly, I don't know. Your best bet is to call Optus (133 937) and ask "if I was to cancel my contract right now, how much will my last bill be?" you'll get the figure.
The process works like so: You go to Telstra, tell them you're with Optus and want to go to Telstra. Telstra ports your number away from Optus and when this happens, Optus go "looks like they left, cancel contract" and their system cancels your contract. You are then sent a final invoice from Optus for however much you owe them. Pay it and you're done.
SUMMARY: You don't need to call Optus to cancel your contract or anything. In fact, you never have to talk to Optus ever again.
Step 2 - Getting the iPhone
Some Telstra stores are opening across Australia at midnight. See here for a list. Bluntly, if you want an iPhone on the 30th of July, you need to line up and wait. I predict that there will be no iPhones available to buy, from any carrier, anywhere in Australia, beyond noon on the 30th of July. So if you aren't prepared to devote yourself to lining up, or can't due to work, then you probably are not going to get an iPhone on launch day. Do not expect to walk in on your lunch break from work and pick up an iPhone 4.
You can also line up at an Apple store (which open at 8AM) and go on a Telstra (or anyone else) contract there. Apple will have reps from all the telcos (Telstra, Voda, 3 and Optus) in their stores on launch day.
SUMMARY: Line up as early as you're prepared to. Always remember that there will be someone who wants that phone more than you. Don't be pissy if you missed out. You just weren't dedicated enough.
Step 3 - Signing the Contract
You're finally in the store (after waiting hours in the cold) and they still have stock left, hooray! Now you have to sign a new contract with Telstra. Know which plan you want before you go in. Pricing is listed here. There's nothing worse than someone wasting the sales reps time deciding on a plan, when there are dozens (if not hundreds) of people behind them waiting for an iPhone 4 too!
Pick a plan that suits you - get your Optus bill, work out how many calls you made, and how long those calls went for - then get how many SMS you made and how much data you used, then pick a plan accordingly.
You can also add on data packs to give yourself a boost if you need more data than the plans provide (pricing here). Data packs are not contracted, so you can cancel them at any time if you decide you aren't using them, or add them on at any time if you notice you're using more than you planned.
So you know what plan you want, you know if or which data pack you want. You need to provide some ID. Telstra do NOT take leaners permits (as I found out the hard way). Here is Telstra's list of approved ID. You need 100 points. Drivers licence + credit card is the usual combo.
You will also need your latest Optus bill. This has on it your account number so Telstra can port you from Optus to Telstra. Telstra does everything to get your existing number and cancel your Optus contract. You don't need to do any of this manually.
You'll sign some forms and the usual crap and then be given a Telstra micro SIM. You'll pay any up front costs if your plan is like that. You're done. Leave the store and gloat amongst your friends that you have an iPhone 4 and they don't.
It will take an hour or so at most (hopefully not too long) to get your existing number on the Telstra network. Pop the microSIM in your iPhone 4 and sit tight. It will automatically start working when the number has been ported across. Your Optus SIM will still work in your 3G/3GS (so you can still get phone calls on your number) until the moment your Telstra service starts working.
SUMMARY: Most issues with new contracts arise from not having the correct ID, not having your existing account number ready (bring your Optus bill in) and owing some other telco money and your credit rating sucks (be sure to pay anyone you owe money to before July 30th).
Step 4 - Bundling with Existing Telstra Services
Do you have existing Telstra services? Particularly a landline? If you do, put them on the same bill and you'll get a discount, or a bonus. It all depends on what you have already (e.g: if you have a Telstra landline, you get 50 free SMS a month). Full details are on the Telstra website. If you're on a Telstra bundle already, add your mobile to that bundle and get $10 off the plan price. This stuff doesn't have to be done at the same time you si
SUMMARY: Look in to bundling all your services (telephone, internet, Foxtel, other mobiles in your family) and you might save a fair bit of money and have everything on a single bill instead of spread out over 3-4 different companies.
Hope this guide helped! Fire away with any questions!