Shares in Research In Motion fell 4.3 percent to their lowest level in almost six years after Apple CEO Tim Cook said that more than 90 percent of Fortune 500 companies are testing or deploying the iPhone and iPad.
The Canadian smartphone maker's stock had jumped nearly 10 percent in the morning as talk that it had hired an investment bank revived speculation that the BlackBerry maker could become a takeover target.
But the stock gave up those gains as Cook spoke, and by 2pm RIM shares were as low as $19.43 on the Nasdaq. It was the first time the shares have dipped below $20 on a stock-split adjusted basis since late 2005.
RIM's BlackBerry has long been the default device for mobile business communication, but rival devices have whittled away at that lead.
Canada's largest wireless carrier, Rogers Communications, said it was launching a program to enable corporate customers to use Apple and Google Android devices to send secure business email.
RIM's shares jumped last week on chatter that activist investor Carl Icahn had taken an interest in the company and would use the position to agitate for change.
RIM's shares have slumped more than 60 percent this year amid a series of profit warnings and dismal sales of its PlayBook tablet computer, which the company had hoped would compete with the hugely popular iPad.
(Reporting by Alastair Sharp; editing by Janet Guttsman)