Research in Motion, the Canadian company that sells the BlackBerry mobile email device, reported revenue growth of 84% for its most recent financial quarter yesterday.

Revenues rose from $1.88 billion in the fourth quarter of the last financial year to $3.46 billion in the same period of this year.

Profits, meanwhile, were up by 25%, from $412.5 million to $518.3 million. That came as some surprise for investors, as the company had issued a profit warning in February. Shares rose 20% on the news.

Although more modest than the three-digit revenue growth rates it has seen in the past, RIM’s performance in the most recent quarter will assuage fears that the company’s business is in danger of serious disruption by new entrants to the smart-phone sector, especially Apple’s fashionable iPhone device – for now at least.

And unusually for a technology company, RIM is optimistic about the near future. It expects to add nearly four million users to its 25 million-strong subscriber base in the coming quarter.