I believe in China.

I have no doubt that this nation of 1.35 billion consumers will continue to lead the global growth boom over the next several decades. In addition, I want to share with you an underserved Chinese market that will likely explode over the next several years. There are several companies poised to capture this consumer wave that has swept over the Western world but is in its infancy in China.

Although China might not see a double-digit economic growth rate again, its current growth in the mid-single digits appears sustainable with continued government support. In the most recent quarter, growth sank a two-decade low of 7.5% -- but compared with any other economy, this remains a very impressive rate. China's leading economic figure, Premier Li Keqiang, has vowed to keep growth at 7.5% or higher, though it's important to note that other Chinese officials have forecast lower growth over the next several years.

The truth is, the actual growth rate doesn't really matter much for investors. In fact, the International Monetary Fund (IMF) recently indicated that slowing growth will actually lead to a higher quality of growth, which in turn will boost employment, income and consumption. The IMF goes further by projecting that the higher quality of growth will lead to China surpassing the United States as the world's largest economy by 2030.

The most exciting and potentially profitable forecast I found in the IMF's data is that with successful reforms, per-capita income in China could climb to 40% of the U.S. level by 2030. Think about this for a minute: a huge population with spending money in its pockets. It seems to me that this potential could not help but lead to a bull market the size of which has never been experienced in the history of mankind.

The opportunity I'm referring to is maturing in the Western world, but has just begun in China. If you haven't guessed, I'm talking about smartphones.

What I learned from a recent Business Insider Intelligence report is truly eye-opening in terms of scope and investment opportunity. The report shows that while the Chinese cellphone market is mature with slowing growth, the smartphone niche is rapidly expanding. This leads to growth in 3G subscriptions.

While China Mobile (NYSE: CHL) is the lead player in overall mobile subscriptions, it is lagging in smartphone subscriptions. Only 25% of China Mobile's clients are smartphone users. The reason for this is very interesting. It is because China Mobile's market is rural China, where people simply don't have the disposable income for smartphone data plans or 3G service. In addition, China Mobile's 3G network is substantially slower than the other major carriers' networks.

Two lesser-known companies are leading the smartphone data carrier revolution: China Unicom (NYSE: CHU) and China Telecom (NYSE: CHA). The Business Insider report forecasts that within the next year, smartphone sales in China will overtake sales of regular cellular handsets. Both China Unicom and China Telecom have a huge lead on China Mobile, with 45% of their subscribers being smartphone users.

As smartphone use increases in China, China Mobile's slow speeds will place it even further behind the competition of China Unicom and China Telecom.

Risks to Consider: Investment in any Chinese company through American depositary receipts (ADRs) is a risky proposition. Sketchy finances, combined with the heavy hand of government, can derail even the most promising companies. Although things are improving, the great opportunities in China carry similar risks.

Action to Take: I like both China Telecom and China Unicom as long-term investment vehicles. My choice between the two would be China Unicom. Investors in these ADRs should be prepared for volatility, along with the growth, and have at least a five-year investment horizon.