My beloved new 'wife' is slightly more than a month old now and it has changed a lot since: I've installed lots of apps in it to justify its PDA capabilities, I've also adorned it with themes to get away from the default boring black blank theme, and most of all, I've upgraded its firmware to the latest 1.1.4 and have software unlocked it.
A lot of my friends asked me what is the best way to unlock the iPhone and at the moment there're a few software which help you to do that: ZiPhone, iPlus and iLiberty+ (which is actually a result by merging iPlus with iLiberty and therefore running the same engine as iPlus).
I would recommend using iPlus at the moment since iLiberty+ is still new and there were reports that some users were not able to save their Preferences Settings on their phones.
As for ZiPhone, version 2.5-2.6 of the software created some irreversible damage onto the phone which involves the IMAC address (big deal ppl) as what it did was that it set all phones unlocked with the software to have the same IMAC address (it's like everyone of us having the same IC no. That's a BIG DEAL!!! No, we don't want that).
Another thing is that ZiPhone uses the RAMdisk method to unlock the phone by loading everything into the memory of the phone and runs the unlocking from there - very risky as there's a chance that the files might get corrupted.
Also, if you have an iPhone with Bootloader (it's like the BIOS on your computer) v4.6, ZiPhone will downgrade it to 3.9 so that you can use the Locate Me in Google Map as well as to enable some hosts of stuff. But the problem is that once you have 3.9, you can't reset it back to 4.6! This is not good as future apps/firmware might require 4.6 to work. Unless they could find a way to upgrade it back to 4.6, the solution (or rather the damage) is irreversible. By using iPlus/iLiberty+ however, the software will downgrade it to 3.9FakeBlank and therefore, you could restore it back to 4.6 in the future if the need arises.
Hence, at the moment, iPlus and iLiberty+ seem to be the safer ways to unlock your precious Jesus phone.
This post is of no intention whatsoever to condemn/despise any method or software, but to present my humble personal opinion on the safest and hassle-free way to unlock the iPhone and also based on the feedbacks by users in some online forums. In fact, I do admire and am grateful for these developers who created unlocking software for us so that we could use the iPhone without being tied to a certain telco (round of applause to these guys and let us all drink to them...YAAAAAAAAAAAMMMMMM SENG!!!!! :-) ). But care has to be taken as any mishap might cause your iPhone to turn into an overpriced iPod Touch or worse, a door-stopper :-p
Go here for the guide to unlock the iPhone using Windows. The guide for Mac users could be found on the website too, just click the correct guide, that's all. Although it's a depreciated guide, but this method has been tried and tested by many users and has been proven to work so far. If you are daring enough, you could try unlocking with iLiberty+. It might has been updated to fix those bugs i mentioned. Once you've unlocked the phone, go here to look at the apps are available for you. Basically, these are the 2 websites that you need to go to for updated news about the iPhone (unlocked one that is.....:-p). Happy iPhone-ing and Unlocking :-)