Shares of Research In Motion (Nasdaq: RIMM) climbed nearly 5% higher yesterday, and Reuters and Bloomberg are pegging the gains on speculation that Carl Icahn is buying into the struggling smartphone maker.

It's certainly believable rumor mill chatter. RIM fits the profile of a typical Icahn pick as a former darling trading at a price point that didn't seem possible just a couple of years ago.

However, he better not think that simply shaking up the boardroom will cure RIM's ills. The BlackBerry maker can't go back to where it once was because that place no longer exists.

Sure, RIM continues to grow its base of BlackBerry users, now up to a record 70 million smartphone owners. However, there's more here than meets the black eye.

RIM posted larger declines in revenue and earnings in its latest quarter than Wall Street was expecting. RIM is shipping fewer BlackBerry handsets -- and far fewer PlayBook tablets -- than analysts were targeting, and this isn't something that Icahn can change.

Apple (Nasdaq: AAPL) and Google (Nasdaq: GOOG) continue to eat into RIM's once-impressive market share in the smartphone space. Microsoft (Nasdaq: MSFT) is so confident in its mobile operating system that it's willing to pay billions to Nokia (NYSE: NOK) to champion the platform.

Icahn can't orchestrate success. There is no turnaround here. The only realistic endgame for an activist investor in RIM is to smoke out an outright buyer, but who would dare acquire RIM after seeing Hewlett-Packard's (NYSE: HPQ) fiasco with Palm play out?

Three years ago, Canaccord Adams analyst Peter Misek was fairly certain that Microsoft had a standing order to buy RIM if it ever dipped below $50. Well, RIM fell through $50, $40, and $30 without Mr. Softy swooping in on bended knee. It's unlikely to happen now that the world's largest software company has a 10-figure bet on its own horse.

So what can an activist really accomplish at RIM? It's true that the valuations are ridiculously cheap these days, but everybody is fully aware of the headwinds that will continue to challenge RIM and intensify in the future.

Are you sure you know what you're getting into here, Icahn -- if you're getting in at all?

If you want to see how the smartphone battle plays out, follow the relevant companies by adding Google, Research In Motion, and Apple to My Watchlist.