The explosive growth of cell-phone subscriptions indicate that emerging markets could rebound in the coming years – giving investors a heads up of impending profits.

We’ve always relied on the “Cell Phone Indicator” as a forecasting tool for potential economic growth in emerging economies. Now, based on a recent report, it looks like our long-term confidence in these nascent markets will hold fast despite the current malaise that has gripped the world.

Our informal “Cell Phone Indicator” posits that mobile communications have historically signaled the growth of a new economy. In many countries, cell phones are the only form of communications for an individual. Armed with a mobile gateway to the outside world, cell phones are literally the seeds to entrepreneurial growth. Craftsmen, farmers, fishermen, retailers – just about anyone involved in a small business – can order and ship products, and even exchange money, using these wireless, digital devices.

On a grander scale, widespread cell phone adoption indicates significant investments in national infrastructures. Towers, power stations and repeaters are installed to facilitate economic growth. From these, come the roads, harbors and bridges to help carry the goods from these wireless transactions.

Investors who ignore cell phones as an economic indicator do so at their own peril.

Now we have some new numbers just released that forecast explosive cell-phone growth in emerging markets. If these predictions are even remotely accurate, we can expect more rapid growth in many third-world countries that could harkens back to good old boom-town days of the so-called Commodity Supercycle.

According to Informa Telecoms & Media’s Global Mobile Forecasts, annual revenues from the global mobile market will top $1.03 trillion by 2013, when the number of subscriptions worldwide will have risen to more than 5.3 billion. The implications for investors are truly profound.

It took more than 20 years to reach 3 billion subscriptions, says the report, but another 1.9 billion net additions are forecast in just six years, with the global total nudging past the 5-billion by 2011.

Total annual revenues from mobile operators are expected to grow by over 30%, surging from $769 billion in 2007 to $1.03 trillion six years later.

Informa Telecoms & Media forecasts 78% of global net additions between 2007 and 2013 to come from markets in Asia Pacific, Africa and Latin America.

Five markets — India, China, Indonesia, Brazil and Russia – will account for 47% of those 1.9 billion new users.

By contrast, mature markets in North America and Western Europe will contribute just 8% of total global net adds, reflecting the high level of saturation in these markets.

The underlying message here is that we could see a real grass-roots growth in many of these countries – the kind of economic expansion that often slips under the radar of the major news outlets.