Apple’s iPhone 4 is officially launching tomorrow, and some lucky iPhone 4 customers are even getting their hands on the device today. If you’re planning on lining up on Thursday to get your own iPhone 4, or even if you’ve already pre-ordered a new iPhone, check out this quick rundown of everything you need to know to survive the next few days of iPhone mania.

I’ve got tips for where to find an iPhone 4, where you can sell off your old iPhone devices for a tidy sum, and some handy information about iOS 4, the iPhone’s newest operating system. So check it out, bookmark it, or throw it on Instapaper to have this handy reference guide readily available; you’ll be glad you did.

How good is the iPhone 4?

Overall, most critics have been impressed with Apple’s new smartphone, and some reviewers are reporting extraordinary battery life on the new device. You can read PCWorld’s iPhone 4 review, and also check out this visual tour featuring a side-by-side comparison of the iPhone 4 and iPhone 3GS.

If you want to get a sense of what the rest of the technology world is thinking about the iPhone 4 check out this breakdown of five early iPhone 4 reviews.

Where can I dump my iPhone 3GS for a good price?

If you’ve got a year to go on your iPhone 3GS contract, but still want to get an iPhone 4 this weekend, you might be thinking about selling your device online to cut down the upfront costs of buying an iPhone for full price.

A user on AT&T’s forums named tevisb claims to have sold an iPhone 3GS on ebay for $375. After paying ebay’s seller fees including the auction site’s 9 percent cut of the final sale, tevisb was left with about $370. That’s a pretty good chunk of change to help pay for the iPhone 4’s non-subsidized prices of $599 (16GB) and $699 (32GB).