How flat-rate pricing changes the future of cellular

"I think they'd have to be at least at $70 or $80 [per month] to make an impact on the market," Hart said. "Anything more than that won't make much of an impact." And, they could even go lower, Hart and the others said.

While a price war is possible, Gartner mobile analyst Ken Dulaney said that AT&T, Verizon and T-Mobile may not follow suit if Sprint goes too low.

"They won't follow Sprint," Dulaney said. "They believe they have other attributes that will keep Sprint at bay. AT&T can say, 'look at all our phones, and we're worldwide.' And the typical Verizon customer typically uses them for their coverage."

Trend 3: Abandoning land lines

Dulaney pointed to a major trend that flat-rate pricing could help accelerate: users abandoning their land-line phones and using only cell phones. That should start occurring after flat-rate prices come down.