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Expectations that AT&T will lower the cost of wireless service for Apple's iPhone are growing. A $20-a-month data plan with limited access is a possibility for the exclusive U.S. iPhone service provider.

AT&T's monthly plan for the iPhone is currently $69 plus taxes and fees and includes a $30 unlimited data plan. A comScore study found that 43 percent of current iPhone users have incomes above $100,000, so AT&T needs a lower price for it and Apple to grab a larger share of the smartphone market.

Over the last two years, Apple and AT&T have collaborated on one of the most successful product launches in recent history, using a wave of positive press to help sell more than 17 million iPhones.

But the three-year anniversary of the iPhone is fast approaching, and as phone manufacturer Motorola can attest, few high-tech devices remain shiny and compelling forever. The seemingly endless number of apps available for the iPhone may help delay consumer ennui, but Apple -- and particularly AT&T -- are clearly worried about the rising buzz for new entrants in the smartphone category.