Battered by a long-running patent dispute and fears of competition, Research In Motion ( RIMM) has had one solid defense in recent quarters: its standout growth rate.

Now that shield may be going away.

The company warned on Wednesday that subscriber additions to its BlackBerry service will come in lower than anticipated in the next two quarters. RIM blamed the shortfall on the late rollout of two new BlackBerry devices.

But investors and buy-side analysts aren't buying the argument. Instead, they see something much more portentous: the beginning of an inevitable slowdown in RIM's growth rates. If they're right, the development could have big implications for the company's stock price.

Indeed some former bulls have recently gone short RIM shares and others are considering doing the same.

You can put Scott Rothbort, president of LakeView Asset Management and a contributor to TheStreet.com's sister site Street Insight, in that latter camp.

"I don't see where this company is going," says Rothbort, who currently has no position in RIM's shares. "There's no good news over at RIM."

Instead, on Wednesday the company offered more bad news. The company said it expects subscriber additions in its current quarter will come in 8% lower than its expected range of 680,000 to 710,000. For its fourth quarter, the company expects subscriber additions to be 3% lower than its previously forecasted range of 775,000 to 825,000.

Shares of RIM closed regular trading on Wednesday off 80 cents, or about 1%, to $66.28. Earlier in the session, following the announcement, they were off as much as 7% before bouncing back.

Some investors and analysts are beginning to believe that things are likely to get worse for RIM. The slashed forecasts mark the second time in three months that the company has had disappointing news on the subscriber front. Subscriber additions in the second quarter came in at the low end of the company's expected range.

And while the subscriber shortfall may not hurt near-term financial results, it could affect future revenue and earnings. Fewer subscribers now mean lower revenue later and potentially fewer devices sold.

Some analysts doubt that the problem with subscribers really has to do delayed devices. The new handsets are more likely to have been appealing to current BlackBerry subscribers looking to upgrade their handsets rather than potential customers, says one buy-side analyst, who asked not to be named.

"This just feels like they're just trying to resize expectations," said the analyst, whose firm has no position in RIM's shares. "I don't think the market is as big as what they thought."

Others argue that the company is seeing the effects of its ongoing patent battle with NTP. RIM has been found to be infringing NTP patents covering wireless email systems, a decision that has been upheld by an appeals court.

A federal judge is now determining whether to enforce a settlement the two companies reached in March, which later fell apart. Assuming he rules there was no settlement, RIM faces the prospect of paying millions of dollars in penalties to NTP -- or even having its BlackBerry service shuttered in the U.S., its biggest market.

The case seems to be distracting management from running the business, say some analysts. But, potentially more importantly, the case may be scaring off potential customers, they say.

In deciding whether to sign up for BlackBerry service -- or with one of RIM's competitors -- enterprise customers are likely weighing the possibility that their service could be shut down within months, or that they themselves might be forced to pay royalties to NTP, some analysts worry.

"This dispute has become a big distraction," says Jay Somaney, a hedge-fund manager with TSG Capital Partners and founder of GlobalTechStocks.com. "In my opinion, nothing good is going to come out of this thing," adds Somaney, who is short RIM shares.

RIM's legal setbacks have come at an inopportune time. On both the hardware and software sides, competition for RIM's BlackBerry offerings seems to be heating up. Palm ( PALM), for instance, has found success with its Treo smartphones, which offer wireless email and other features found on RIM's devices. Meanwhile, in recent months, industry giants Nokia ( NOK) and Microsoft ( MSFT) have rolled out software that competes with RIM's BlackBerry service.

"You're seeing Palm and Samsung taking their market share from them, which I don't think they're about to get back so quickly," says Rothbort, who has no position in either company.

And some observers see things only deteriorating from here. What has set RIM apart is its push-email service, which instantly syncs mailboxes on mobile devices with corporate email servers. But with the increasing prevalence of high-speed wireless networks, that differentiation is starting to matter less and less, argues Dave Schamens, a buy-side analyst at Invictus Funds.

Such networks will allow fast delivery of email no matter what the protocol, he argues, meaning that customers won't necessarily have to use RIM's system. Moreover, such networks will allow for much more sophisticated data and applications, Schamens says. Essentially, the mobile device is becoming the new desktop computer, he argues. And as that transition is made, Microsoft, not RIM, will be the best positioned to take advantage of it, because of the software behemoth's entrenchment on desktop computers and among corporate customers.

"The bottom line is the competition is closing in on RIM," says Schamens, whose firm is neutral on RIM owning shares in the company and put options. "RIM will just become another product manufacturer."

And there's not much special in that.