The two brands are duking it out over customers on Twitter. In January, AT&T took out attack ads against T-Mobile, weeks after T-Mobile's CEO got kicked out when he crashed an AT&T industry party.
Now, their latest skirmish is a chance for consumers to snag new deals on a smartphone plan.
"Everyone who wants a smartphone has one," said independent technology analyst Jeff Kagan. "Now we're seeing carriers battle with to win each other's smartphone users."
For the next wave of wireless industry transformation, said Kagan, that's going to mean competing on quality, customer service, and price.
(Read more: AT&T cuts wireless data charges for individuals)
The most recent round of arrows flew Saturday when T-Mobile announced it was doubling the data for customers on its "Simple Choice" plans without increasing the prices. The next day, AT&T responded by cutting the price on its "Share Value plan" by $15.
To sweeten the deal and help it poach more customers, T-Mobile has offered to pay customer's early termination fees if they leave their carrier, no contract required. AT&T is also not requiring a two-year agreement on its comparable plan.
So between the "Unlimited" data plans Sprint has out, and Verizon's "More Everything" plans unveiled last month, where's the best place to go?
The below chart looks at a price-conscious consumer who wants unlimited talk and text, uses the average amount of data—about 1GB—and doesn't want to pay more than $70, around what T-Mobile and AT&T have on offer.
In this user scenario, T-Mobile wins on pure price and data. Another benefit is that instead of racking up overage charges after you exceed pass your high speed data allotment, it shunts you to a slower network for data.
While that may sound enticing, check the coverage maps before making any switches. T-Mobile's smaller network was rated the lowest in overall performance in a recent RootMetrics test of the big four networks.
(Read more: Sculley targets India's smartphone market)
But if that price war doesn't have enough bloodshed for your wallet, "freemium" programs can offer even deeper savings. Services like "Line2" and "Upptalk" can be had for $15 a month, offering both calling and data. Another contender, "Freedompop." is free but has a footprint limited to roughly a third of the nation. Several freemium companies also let you earn more credits or data by watching ads or referring new users.
The services definitely have their quirks, so be sure to investigate the terms and conditions before porting over your number.
Because whether at the high or low end of the smartphone plan market, sometimes you just get what you pay for.
—By Ben Popken of NBC News