T-Mobile US added 2.75 million customers in August, the largest number of monthly subscriber additions in its history, the carrier announced at a company event on Wednesday.

Led by quirky Chief Executive John Legere, the third-largest wireless operator in the U.S. has turned around years of subscriber losses through aggressive promotions in the past year and a half.

The company also announced that it will enable its phones to allow customers to seamlessly be transferred onto WiFi networks where its network doesn't reach. While rivals Verizon and AT&T networks stretch almost across the country, T-Mobile's network is clustered around urban centers.

Current subscribers can trade in their devices for phones enabled with Wifi connectivity when they sign up for the company's early upgrade program.

The carrier is also offering a free personal CellSpot site customers can place wherever they lack coverage.

The move comes the day after Apple Inc. announced it will release an iPhone programmed with technology to allow automatic shifts between WiFi and carrier networks.

"Apples announcement set the road map for this," said Legere at the event. "It gives us the option to turn the wireless industry on its head starting with trashing the old rules about where cellular ends and WiFi begins," he said.

T-Mobile customers will also now be able to use the setting to make free calls internationally.

Major wireless carriers have amped up their promotions in the face of the Apple's new iPhone 6 release on Tuesday, in an attempt to poach customers from each other in a nearly saturated market.

Earlier on Wednesday, AT&T announced it is offering customers a $300 credit and a free iPhone 6 when they trade in their old iPhones.

Sprint Corp announced on Tuesday a program that allows customers to lease the iPhone 6 and get the latest iPhone model every two years for $20 a month when they sign up for an unlimited plan.

Verizon Communications will give subscribers who trade in an old iPhone a free iPhone 6 in exchange for a two-year contract.

Earlier in the week, T-mobile announced it will match any deal in the industry.