WATERLOO, Ont. ( TheStreet) -- The mythic Apple ( AAPL) Tablet coming to Verizon ( VZ) has put a dark cloud over Research In Motion's ( RIMM) otherwise sunny skies.

RIM has been enjoying a spectacular front seat ride along the smartphone highway, with new offerings like the Tour and Curve keeping the BlackBerry bonanza bouncing along.

But there's a hazard up ahead, as Apple and Verizon check off the final details on the much-debated, hotly-anticipated touchscreen Tablet device due to hit the road before the holidays.

Apple's Tablet Will Be an iFlop

"We anticipate some potential headwinds in the back half of the calendar year," writes UBS analyst Maynard Um in a research note Monday.

Um points out that the concerns are largely emotional and not yet material. He does note, however, that Verizon is among RIM's top three customers, accounting for between 10% and 25% of the BlackBerry maker's quarterly revenue.

The thinking is that Apple, while currently not a Verizon supplier, could eventually take a few top rungs on Verizon's product ladder.

The arrival this year of the data-only Tablet would be the first Apple device, opening the way for the iPhone next year after the AT&T ( T) exclusivity deal ends. As AT&T discovered, an Apple partnership is a mix of burden and reward.

From a marketing standpoint, Apple tends to take center stage, potentially leaving other phone makers -- RIM for example -- in the background.

The rise of competition in the smartphone arena from players like Palm ( PALM), Apple and even Motorola ( MOT), which will soon unveil phones with Google's ( GOOG) Android operating system, puts new pressure on RIM.

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