When we conducted our first wave of research into stalled growth among former Inc. 500 companies, we were intrigued to discover how many of them had at one time been pioneers in their industry, which (by definition) gave them 100 percent market share. By the time we fielded our study, however, the average market share of these companies was only 16 percent.

That’s not surprising. As any industry matures, increasing competition will carve it up into smaller and more tightly-focused market segments. Still, it’s no fun to climb to the top only to watch your market share decline year after year (just ask GM).

One of the more notable companies currently struggling with this phenomenon is Nokia, the nearly 150-year-old Finnish corporation that became the global mobile phone leader in 1998. Nokia is one of the most powerful brands in the world and has sold well over one billion mobile devices. That’s a lot of phones.

Alas, it’s hard to stay big. In the past few years, as the economy sputtered and competitors stalked, Nokia’s share of the mobile device market began slipping. It was forced to fight off a bevy of low-cost competitors at the volume-driven bottom of the market and the Blackberry and iPhone phenomena at the margin-driven top. In its recent quarterly earnings release, Nokia reported that its mobile device volume was down 19 percent from last year, while the industry was down only 14 percent. That cost Nokia two points of market share, from 39 percent to 37 percent.

The company does have a lot of cash and new products in the pipeline, but it’s tough to fight a multi-front war. As the industry continues to struggle (Nokia predicts a 10 percent industry volume decline in 2009), the company’s smaller competitors are likely to get even more aggressive, whether out of opportunism or desperation.

Nokia’s strategy, according to internal documents, is built to leverage “scale, brand and service.” It will need all three operating at peak performance to keep from sliding further back as the year plays out.