IPhone – What are the high level steps and limitations for unlocking & jailbreaking an original iPhone

I jailbroke my iPhone 4 few weeks ago, specifically for the MyFi, which allows you to tether your 3G connection to your other WiFi-enabled devices (iPad, laptop, etc), without paying $20 to AT&T every month and being limited by 2Gb of data. MyFi is $19.99, but you pay it once and enjoy free tethering after that, especially if you kept your $30 unlimited data plan (I did). Initially beyond that I saw very little reason to use other apps from Cydia store, but now I slowly changing my mind, since I found few real gems.

• SBSettings - gives you quick panel to toggle WiFi, Bluetooth, 3G and few other functions. This is extremely handy, especially when you're trying to preserve your battery (long day on the conference or something) and you don't want to dive into Settings each time you want to turn WiFi on or off. SBSettings is free

• Notified Pro - this is notification management done right. Notifications have horrible usability in iOS and this app ($4.00 for Pro version, but I think they have the light one for free as well) fixes it by introducing notifications list similar to one Android has, which you can activate from status bar or via other customized shortcuts

• Frash - which is Flash for iPhone, right in your mobile Safari. Frankly I haven't use it for anything serious yet (and it doesn't support my favorite Flash game Quadradius), but it's a good app to wow your friends, since everyone knows that there's no Flash on the iPhone and you can always prove people wrong.

• My favorite app IntelliScreen - it's a paid app as well, but it's extremely handy. It gives you a highly customizable lock screen very similar to Windows Mobile's Today screen, so you can look at your calendar, emails, SMS and other info without even unlocking your phone. Really, really handy.

One other thing that I didn't try personally yet, but going to soon is sync with your PC or Mac over WiFi. I hate to do it over a cable.

Now, on the bad side:

• You have to be more careful and knowledgeable about stuff you're installing. That includes both apps (which are, in general, more buggy and may conflict with each other or with iOS) and stuff like official Apple iOS updates that you can't install unless you know that there's a jailbreak for them.

• Cydia store (and others like RockYou app store) are less informative than AppStore and quite often it's hard to figure out what certain app does

• Payment (while they allow multiple ways including AMazon payments and PayPal) is usually much more painful

• Apps quite often are more expensive (think $4.99-$9.99 range), but on the bright side they worth it

Jailbreaking utilizes an exploit in the OS (or in the latest cast, the boot ROM), and injects the payload onto the phone, which is usually a loader to install Cydia, or Cydia itself. Cydia is the source for applications not in the App Store, and once this is loaded, other software can be installed which could modify system files. One such case is Winterboard, which allows you to customize aspects of the UI.

With regards to question 1:

It depends on what happens during the jailbreak. If, for example, you're running the exploit to jailbreak the phone and the battery dies (or the software malfunctions), there's a chance you'll brick it. It's hard to pin a percentage on it.

With regards to question 2:

Since Apple is expecting their software to be running on the phone, it may do some things that could brick the phone. Again, it definitely varies on what has been changed, how the jailbreak was performed, etc. Personally if Apple comes out with an iOS update, I'm not going to just allow it to run. If I want it, first thing I'd do is restore the original firmware via iTunes.