Who needs a moat when you can just erect a huge wall?

This philosophy has long permeated the wireless Internet services market in the United States. Carriers such as AT&T (NYSE:T), Sprint Nextel (NYSE:S), and Verizon Wireless -- a joint venture between Verizon Communications (NYSE:VZ) and Vodafone -- have long maintained a "walled garden" approach to keeping subscribers captive to their own content portals. By restricting customers to a smaller list of approved providers on their own portals -- rather than leaving the entire mobile Web open without bias -- carriers maintain more control over users and the profits generated from content.

Seeing what a great deal this is for the carriers, Chinese wireless providers China Mobile (NYSE:CHL) and China Unicom (NYSE:CHU) have been methodically transforming their service offerings to follow in the footsteps of their American brethren. While other companies in the value chain vocally lament this growth-stifling practice, the benefit to the carriers is obvious -- China Mobile recently reported a 35.5% increase in value-added service revenue that helped maintain its average revenue per subscriber even as average voice revenue per minute dropped 19.3%.

The strategy helps keep wireless carriers from simply becoming a "dumb pipe" that would only charge blindly for mobile traffic to sites such as KongZhong (NASDAQ:KONG). Instead, having control over content allows carriers to maintain premiums for services and gives them enormous power to negotiate lopsided deals with content aggregators and providers.

Since many of the independent content aggregators make a significant portion of their revenue from advertising, a drop in traffic ties in directly with drop in revenue. Other companies on the losing end of the equation -- but to a lesser degree -- are SINA (NASDAQ:SINA) and Linktone. In response, many of the aggregators are already shifting their business models to emphasizing services that have less dependence on the carriers.

This trend reminds investors that the power in the mobile value chain ultimately resides with the carrier -- the one with the direct face to the customer. Without a strong brand and alternative channels to sell content, aggregators in China's mobile market will continue to struggle against this great wall.

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Fool contributor Dave Mock has contemplated a great wall in his garden to keep snails out. He owns no shares of companies mentioned here. He is the author of The Qualcomm Equation. Vodafone is an Inside Value recommendation. SINA is a Stock Advisor pick. The Fool's disclosure policy scales walls faster than a spring monkey on Red Bull.