When InterDigital (Nasdaq: IDCC) closed the door on strategic alternatives, it didn't stay locked for long. Just one month after declaring the search for an exit strategy, the mobile patent wrangler punctuated its fourth-quarter report with a promise to start selling some patents. "As part of our expanded business plan, we also intend to generate cash flow from the sale of non-core patent assets," said CEO Bill Merritt.

That's far short of selling the entire company to the highest bidder, but a significant step in the same direction. Merritt wants to take advantage of the pockets of industry interest that showed up in the process of actually looking for all-or-nothing buyers. Whether by direct sales or joint partnerships, InterDigital wants to extract some money from small batches of patents that don't add much to the top or bottom lines today.

The income statement could use a bit of a boost. GAAP earnings fell 36% year-over-year to $0.49 per diluted share on sales of $77 million, down from $95 million a year ago. Analysts were expecting worse, so the stock is surging today. Still, the company doesn't paint a very pretty picture here.

Making matters even worse, InterDigital burned $10.8 million of free cash in the quarter and a total of $65.3 million in fiscal year 2011. Patent licenses in the red-hot mobile market may sound like easy money, but InterDigital is showing us how tough it really is to make a living this way. The stock has lagged behind the Dow Jones Industrial Index (INDEX: ^DJI) benchmark over the last year, save for a brief respite when the company looked like it could find a buyer.

Investors in Qualcomm (Nasdaq: QCOM) and VirnetX (AMEX: VHC) should take a good look at this object lesson. Though vastly different in size, scope, and maturity, both stocks are resting on the proven or supposed value of their mobile patent portfolios. It's not always an easy road to travel, especially if you don't have the financial safety cushion of chip giant Qualcomm.

Smartphones and tablets are building a trillion-dollar market before our very eyes, and InterDigital is desperately trying to find a foothold in that massive opportunity. Maybe the right strategy is behind another locked door, but it's hard to know until management pulls the handle. Investing in this revolution doesn't have to be difficult; some companies have already carved out their niches.