Even though the iPhone 4 officially only ships today, beta versions of the operating system, iOS4, have been circulating on the web for at least a week.

However, the task of cracking an iPhone 4 is made more complex, Infosecurity notes, by the fact that the ROM inside the phone also needs to be decoded.

According to the developers of the popular Pwnage iPhone unlocking and hacking utility, PwnageTool 4.01 will unlock an iPhone 4, as well as the earlier model, the 3GS, with iOS4 loaded.

The CNet newswire says that PwnageTool 4.01 will work with an iPhone 3GS as long as "it was previously jailbroken with the old boot ROM and you didn't use the Spirit method."

"However, if your 3GS has the new boot ROM, you will not be able to use PwnageTool", says the IT news portal.

"The new hacks only support the official iOS 4 release and not the developer release issued at WWDC", it adds.

For those readers not prepared to pay more than $75 a month for a free iPhone 4, the good news is that the 3GS is reportedly being discounted by retailers who are seemingly keen to sell their existing stocks of the earlier iPhone.

The Mobile Today newswire says that pricing of the iPhone 3GS fell by around 10% during May, although some sources told the newswire that the difference in pricing between the iPhone 4 and the 3GS is not as great as it was between the latter handset and the earlier iPhone 3.