U.S. telco hits back at Verizon with pricey price plan; elicits Twitter-based derision from T-Mobile’s Legere.

AT&T has become the latest U.S. telco to ramp up its unlimited price plan, following a similar move by major rival Verizon earlier this week.

AT&T stopped offering unlimited tariffs to smartphone customers in June 2010. It later began offering them again, but only to customers who also signed up to its U-verse or DirecTV services.

On Friday though, AT&T announced it was making unlimited price plans available to all consumer and business postpaid customers. Prices start at $100 for a single line; extra lines cost $40 per month up to a maximum four. After two months, the price for a four-line package falls from $220 to $180 per month.

"We’re offering unlimited entertainment on the nation’s best data network where and when you want to enjoy more of what you love," said David Christopher, CMO of AT&T’s entertainment group.

Customers can also get unlimited calls and texts from the U.S. to Canada and Mexico, while subscribers travelling to those countries can roam at no extra charge when they add AT&T’s free Roam North America feature to their price plan.

By comparison, Verizon’s new Unlimited plan, launched on Monday, costs $80 per month for the first line, plus an extra $45 per month per additional line, up to four lines.

Just like Verizon, AT&T’s unlimited plan comes with a 22 GB per month fair usage policy (FUP). Once that limit is reached, AT&T reserves the right to restrict the connection speed of these data-hungry customers during periods of network congestion.

AT&T’s announcement elicited a somewhat derisive response via Twitter from T-Mobile US chief executive John Legere.

"T-Mobile offers unlimited. LITERALLY EVERYONE FOLLOWS," he wrote.

T-Mobile US offers its unlimited One plan for $75 per month for a single line, or $160 per month for four lines.