Canadian company Research in Motion (RIM) introduced the BlackBerry wireless e-mail device in 1999, at the height of the dotcom boom.

Looking like a pager and far from intuitive to use, the BlackBerry still became a hot seller in corporate circles.

Users who signed up in the early days became addicted to constant access to e-mail, leading to the device's nickname "CrackBerry".

BlackBerry enables users to read and respond to e-mail on a wireless device small enough to fit into your pocket or handbag. It uses "push" technology, which means rather than having to check an account sporadically, new e-mail is forwarded to the device at regular intervals.

There are now over four million BlackBerry users worldwide, including several thousand in Ireland. O2 signed an exclusive deal with RIM to introduce the BlackBerry to the Irish market in 2003.

Vodafone now also sells the BlackBerry in Ireland and RIM has done deals with other manufacturers, such as Nokia, to include BlackBerry software on their smart phones.