No. Unlocking your phone is legal.

But it is illegal to attempt to make a stolen phone work by changing its IMEI code. If you suspect your handset is stolen then you need to report it to your service provider.

A mobile phone operating system (OS) is software that manages the phone's hardware and allows you to interact with your mobile phone, in the same way as a PC operating system, such as Windows.

There have been instances of criminals tricking phone users into dialing premium rate numbers, and some small scale virus outbreaks on the Android Market, but so far there haven't been any highly prolific viruses or malicious software attacks on mobile phones. 

But, experts are warning that as smartphones become more and more popular, while at the same time relying on fewer operating systems, they will increasingly become more of a target for cyber thieves and malicious hackers.

​Launch in the early 2003, 3G network represents third generation mobile phone networks, offering faster mobile Internet connectivity and Video calling.