A senior investment banker at a major Wall Street firm kept sending out emails on his BlackBerry on Wednesday morning. And they kept bouncing back.

It's one of those things -- you don't realize how important it is to breathe, until you can't do it, said the New York-based banker, who declined to be named because he was not authorized to speak about the subject on behalf of his bank.

The banker is one of millions of BlackBerry users in various regions around the world who have been plagued by service disruptions over the last three days, with North American users of Research in Motion's popular handheld device being the latest to get hit on Wednesday.

Indeed, Wall Street honchos and others who tend to spend more time on their BlackBerry than perhaps with their families were left frustrated at the service disruption -- a sentiment that does not bode well for Research in Motion.

The disruptions were the worst since an outage swept North America two years ago, and analysts said it could ratchet up the negative sentiment toward a company already losing market share to rivals such as Apple and Samsung.

Research in Motion advised clients of the outage in the Americas and said it was working to restore services. The company wasn't immediately available to comment on this article.

The disruption comes on top of increasing demand from bankers to be allowed to use other devices on company networks. Some do not want to carry two phones, and some prefer tablet computers such as iPads over laptops.

Banks also have an incentive in allowing employees to use their own devices, as it can save on costs that come with the company paying for the BlackBerry and the service plan.

One London-based banker, who advises telecom and technology companies, said he has been increasingly using an iPad with clients during pitches but was worried about data security.

I only use my iPad for publicly available information at the moment because we are not yet sure about security for nonpublic and sensitive information, said the banker said, who wasn't authorized to speak publicly about the subject.

One of Blackberry's main selling points has been Research in Motion's top-tier security features.

But mobile device management companies such as Good Technology and MobileIron are offering alternatives, allowing some banks to start letting employees use other devices like iPhones, iPads and Google Inc's Android-based phones on the company's network.

Credit Suisse, for instance, allows employees to connect to other devices, while Barclays Capital allows some employees to use iPhones and iPads. Standard Chartered switched from BlackBerry to iPhones for many users several months ago.

At Sagent Advisors, an independent investment bank in New York, 10 percent to 15 percent of the users have switched to iPhones, while another 10 percent to 15 percent have taken up Android devices.

It is still mostly BlackBerry but quickly moving away, said Terrence Barron, Sagent's head of marketing and communications. Over time there has been much more of sliding over to Android devices and iPhones for us.

Still, Blackberry remains ubiquitous on Wall Street, and some bankers said they prefer the device over others when it comes to work.

One Houston-based investment banker who focuses on energy sector deals said while Wednesday's disruption was frustrating, he felt it was not frequent enough to force a change at his firm.

If BlackBerry were down every other day it would be a pretty big issue, the banker said. It just forces you to actually call your assistant. It's like the old days, when you had to talk to people.

The banker, who requested anonymity because he was not authorized to speak to the press, said he also carries an iPhone for personal use.

(Reporting by Paritosh Bansal in New York and Victoria Howley in London; Additional reporting by Michael Erman and Soyoung Kim; Editing by Bernard Orr)

Apple inc. Blackberry Investment