Take your world by Storm is what Research In Motion or RIM told cell phone users when they launched their first touch screen smart phone in 2008. But users were up against a hurdle when they discovered that the phone was SIM locked by default.

It wasn't a new problem. Other phones before the Storm were also locked and service providers were initially sticky about unlocking phones when the arrangement was first introduced.

But what exactly is a SIM lock? And why do handsets come with a lock? Is it for security reasons? Not exactly. Economics rather than security concerns were uppermost on the minds of service providers when they introduced the facility that proved only a hindrance to customers.

A SIM lock basically means that you can use your phone with only a designated service provider. If you do attempt to switch network carriers, your phone will simply say ?Insert the correct SIM card?.

A SIM lock is also called a network lock or subsidy lock can apply to different parameters. This means phones can be locked to a specific country, service provider or SIM type.

Locking a handset to a specific service provider assures the carrier a fixed amount of revenue every time a handset is sold.

All you have to do is call up your service provider and they will unlock your Storm for you. Or you can send them an email. What you will get is a code that you need to type into your phone and it will unlock instantly.

In the US, there is a rider, though. There are two GSM carriers ? T-Mobile and AT&T Wireless. Both will allow you to unlock your Blackberry Storm if you have an active account and have paid your bills regularly for a minimum period of 90 days. T-Mobile, however, insists that you pay the full retail price for your handset (no discounts) and offer proof of purchase.

But there are no laws governing the locking of phones in the US and the UK so you can't approach the courts of your network carrier refuses to unlock your phone. On the other hand, countries like Singapore bar providers from locking handsets.

Apart from assuring a minimum fix amount of revenue for service providers, phones are SIM locked because customers often sell expensive cell phones after unlocking them at prices higher than the retail price. To guard against this practice, network operators make it compulsory for customers to buy large amounts of airtime with the handset to recover the cost price of the handset.