Itching for a comeback, T-Mobile is assuming a new-challenger attitude as it kick-starts a brand refresh by toughening up its pink-clad TV spokesperson. Talk about TV everywhere: The national buy will be in broadcast and cable TV, Hulu, YouTube and mobile as well as print.

Carly Foulkes, the leggy brunette who has starred in T-Mobile's ads since 2010 and been dubbed by some a DVR-proof pitch personality, is trading her usual frocks for biker leather as the wireless carrier looks to halt mass subscriber defections and uncertainty following AT&T's failed takeover bid. The commercial, "Alter Ego," makes its debut this week. It finds Carly, after tearing up her closet, emerging in a black-leather jumpsuit and riding away on a motorcycle.

Internally, the spot [below] is called "No More Mr. Nice Girl."

"Clearly 2012 is a rebuilding year for T-Mobile," said Peter DeLuca, senior-VP brand, advertising and communications. "We need to get the brand back out there and get consumers to take another look."

The fourth quarter was particularly tough for the company, owned by Deutsche Telekom. As its three major competitors, Verizon, AT&T and Sprint, offered the brand-new Apple iPhone, T-Mobile (which still doesn't carry the iPhone) lost 802,000 contract customers. The No. 4 carrier by subscribers is also looking to set a new course after AT&T's $39 billion takeover bid was foiled by regulators late last year.

In February, during T-Mobile's first earnings call since the thwarted deal, President-CEO Philipp Humm said that T-Mobile intended to spend an additional $200 million in advertising.

"The pending AT&T deal negatively impacted customer satisfaction and brand perception in 2011, which is why we believe it is time to reinvigorate the challenger strategy and to relaunch the brand," Mr. Humm said.

T-Mobile spent $517 million in U.S. measured media last year, according to Kantar Media. Even with the extra ad funding,

T-Mobile will probably be outspent in the high-stakes wireless market. AT&T, for example, spent $1.3 billion on its consumer wireless service last year, according to Kantar.

Despite its smaller budget, T-Mobile ads have seemed to cut through the clutter, thanks largely to Carly, the only current spokescharacter for a mobile carrier who's easily recognizable.

Ads featuring biker Carly, from longtime T-Mobile agency Publicis, Seattle, are intended to equate the brand with speed. The single-biggest thing consumers are looking for in their next smartphone is faster 4G connections, Mr. DeLuca said.

"Before she was this approachable character; now we need to show the other side: She wants speed," he said. "I have to communicate as a challenger that we have 4G."

But that need for speed will also bump up against others' claims about their connections. All four major U.S. carriers tout 4G networks, even though they use different technologies and are in varying phases of updating. That casts "4G" as a marketing catchall meant to convey "faster" rather than any one standard.

"What consumers understand about 4G is it means 'faster' and 'I get to do more on my network,' " Mr. DeLuca said.

T-Mobile has been claiming for some time that it's the U.S.'s "largest" 4G network, even though it has just begun investing another $1.4 billion to build its Long-Term Evolution Network -- the technology that Verizon, for instance, uses for its 4G service.

Carly's new look will be rolled out in a national media buy concentrated in the next two weeks via Publicis Groupe 's Optimedia. T-Mobile's 2,000 retailers will also feature the new Carly.