A major concern at NTT DoCoMo Inc., Japan's largest mobile carrier, is to avoid becoming a "dumb pipe," a telecommunications highway that merely carries data and voice communication between devices without offering much in terms of additional value.

It's a legitimate concern in the era of the smartphone which has diminished the role of carriers while increasing the strain on networks to handle massive amounts of data. In the pre-smartphone age, DoCoMo controlled nearly every service within its network from offering ringtones to browsing Web sites.

DoCoMo's move reflects one way to tackle what is becoming a common problem for carriers worldwide. While the operator's networks are growing crowded from the proliferation of downloaded or streamed content, carriers get no revenue from purchases made in Apple Inc. AAPL +0.79%'s iTunes store or Google GOOG +0.06% Play.