NEW YORK ( TheStreet) -- Words like détente and duopoly are regularly used by consumers and industry skeptics to describe the telecom sector, which is dominated by giants AT&T ( T) and Verizon ( VZ), as second tier players like Sprint ( S), MetroPCS ( PCS), Leap Wireless ( LEAP) and T-Mobile USA struggle. Despite moving to usage-based data pricing in 2011, AT&T and Verizon continue to add to their market dominance. But paranoia cuts both ways. Both carriers have spent billions to build networks to handle rising smartphone data loads, all with an uncertain payoff that's tempered by the safety of their 5% dividend yields. Conflicting fears of concentration and uncertain capital investment returns in the telecom sector have now evolved with Verizon's move to a "share everything" plan, which allows families to bucket mobile devices, in addition to talk, text and data usage onto one bill. As Investors weigh a fast changing industry, they should focus on carrier relationships with Apple ( AAPL) as an early read on whether AT&T and Verizon are primed for rising returns on their network investment, or whether their feared 'duopoly profits' will fizzle. Verizon's pricing change indicates that it is focusing on adding smartphone and tablet devices to its network, while connecting phone bills directly to data usage, over a mélange of data, text and talk. When AT&T follows suit, both carriers will need to prove that device-based network growth -- led by smartphones like the iPhone -- can be done profitably. Meanwhile, headwinds like subsidies to gain iPhone subscribers, consolidation among second-tier players, and the emergence of DISH Network ( DISH) as a competitor loom as threats to AT&T and Verizon. For instance, Craig Moffett, a Bernstein analyst and sector skeptic, questions whether the center can hold on the prospective profits that some fear will gush into AT&T and Verizon, at the expense of consumers. "I think the end of the year is going to look more like the beginning of the year than people think," says Moffett. By that he means a return to challenging revenue per user trends that put wireless investment returns at or below AT&T and Verizon's cost of capital, after they recently posted strong quarters. "The big issue in the industry for investors is whether or not carriers can show better discipline in handset subsidies," noted Moffett, in an interview prior to Verizon's pricing change. Recent attempts by Sprint and Leap Wireless to add Apple devices to their networks have hit shares, as investors anticipate the costs of subsidizing the iPhone. But as Sprint and Leap Wireless add iPhones to pre-paid mobile plans, Verizon and AT&T's expected "share everything" plans may signal a willingness to continue subsidizing new iPhone users, which can cost roughly $500 a device. "Whether or not discipline sticks when a new iPhone arrives on the shelf remains to be seen," adds Moffett. With the pending rollout of the iPhone 5, Jefferies analyst Peter Misek is skeptical that carriers will be able to cut their Apple subsidy habit, even if they can wean off of Google's Android. "We believe the iPhone 5 will be LTE-enabled and that the subsidy reallocation will likely help rather than hurt Apple," wrote Misek in a note to clients earlier in June.