Apple's iOS updates are seeded to developers, often in beta form, before they're released to the general public. This may seem like an impenetrable barrier for some, but very little is preventing you from upgrading early. Here's how to do it.
Acquiring an iOS Beta
The Proper Method: Be a "Developer"
Whether you're actually a developer or not, Apple allows you to pay to be a registered developer for $119. You don't have to make (or even think about making) a single iOS application. All you're required to do is pay the $119 entrance fee. This gets you access to iOS betas for a year and you can download install them as you please.
$119 isn't exactly a great deal to have future access to iOS betas unless you're an iOS fanatic. If you'd still like official access to the beta, however, what we'd recommend doing is rounding up a few friends who would also like early access and splitting the fee. If you can find four other people, that's just $30 each. Because Apple lets you add up to 100 device UDID (the unique device identifier on your iPhone, iPad, or iPod touch) you can easily share a developer membership with others to save some money. With a large number of people, you can get your updates for just a few dollars per year.
If you want to register as a developer, you can do that at the Apple Developer Connection.
It's not hard to locate iOS betas online by simple searching Google for a torrent file. That said, even though you'll be getting the iOS update for free later on in the month, Apple doesn't permit the free downloading of iOS betas. By downloading iOS without Apple's consent, well, you know you're breaking the rules.
If you're not a registered developer and you've somehow obtained a copy of an iOS beta, you may still have some issues. Apple requires that device UDIDs are registered on a developer account to activate the iOS beta. This means that if you install an iOS beta without registering your UDID you may end up with an unusable device. This can be especially problematic because once you upgrade, there's no going back. Well, technically there is but it takes some effort. If you decide to take the risk, be sure you DO NOT restore your iOS device using the beta image. That will pretty much ensure that your iOS device will be locked down. Instead, use the upgrade method (detailed below). If it succeeds, however, it's unlikely the device will need to register with Apple. If it doesn't succeed, don't restore using the update but try to restore using the last available stable release of iOS (as in not a beta, and probably what was on your device beforehand). Again, if you try to restore your device with an iOS beta it will refuse to boot until it is registered with an Apple developer account. You have to use the "Check for Upgrade" route instead.
But what if I screw up? As mentioned above, paying for a developer account with friends is an easy way to save money on getting these early upgrades. But what if nobody likes you (or just doesn't want to pay money for betas like you do)? A quick search will generally turn up a few ambitious individuals who have paid for developer accounts and are looking to make some money. Generally for around $5, they will add your UDID to their developer account so you can easily update without worry. If you happen to screw up the update and lock down your device or just want piece of mind, this is a good alternative to paying the $119 required by Apple. Of course, this is still breaking the rules.
Installing an iOS Beta
Installing an iOS beta is very easy. Connect your device to your computer and open iTunes (if it doesn't open automatically). Choose your device from the iTunes sidebar and you'll see a section called Version. There are two options in that section: Check for Update and Restore.
Restoring will wipe everything off of your iOS device, so you want to avoid that whenever possible. Instead, hold down the option key if you're on a Mac or shift if you're on a Windows PC and click the Check for Update button. You will be prompted to choose an IPSW (iPhone Software) file. Choose the beta you downloaded for your device and click Choose. From there, iTunes will take over and upload the IPSW to your device. The upgrade will start, and if it works you will have the beta up and running in no time*.
* This is not true at all — iTunes takes forever to update. You should go make yourself a sandwich while you wait.