The Blackberry has become the gadget to be seen with

The issue is the US patent for the Blackberry, a handheld phone and e-mail device which has become ubiquitous among the corporate elite.

Research in Motion, the Canadian firm that makes the Blackberry, is appealing against an injunction that effectively bars it from the key US market.

The injunction was won in 2003 by NTP, a firm owned by engineer John Campana.

Mr Campana, who owns 50 patents through NTP, claims Research in Motion violated some of the patents he owns governing wireless text communication.

Fighting back

Research in Motion, whose sole business is making the Blackberry, is resisting strongly.

It has managed to persuade the US Patent Office to re-examine five of NTP's eight relevant patents.

And it has lobbied Congress for support, arguing that Blackberries are vital for national security; all US Congressmen are issued with Blackberries, as a means of ensuring communication during an emergency.

Last year's judgement ordered Research in Motion to pay NTP $54m (�29.4m) in damages, and barred it from the US market, but the injunction is on hold pending some form of settlement.

It is believed likely that NTP is looking for a share of the royalties of the Blackberry, since it is not in a position to begin manufacturing anything similar itself.

Status symbol

At stake is a market worth close to $1bn a year: the Blackberry has a near-monopoly of mobile e-mailing, especially in the US, where text messaging is less popular than in Europe.

The Blackberry, which retails at $300 and upwards, is not a mass-market product; only 1 million are currently in operation, compared with 200 million mobile phones in the US alone.

But its success has been in cornering the very top of the market. It is a must-have accessory among senior executives and celebrities, and has developed a cachet among the emergency services - the New York City Fire Department is connected with Blackberries, for example.

This domination has allowed Research in Motion so far to shrug off the effects of NTP's court challenge. Over the past year, the company's shares have risen fivefold.