The collapse of AT&T’s $39 billion bid for T-Mobile USA leaves the second-largest U.S. mobile carrier with few options to challenge market leader Verizon Wireless. T-Mobile’s spectrum assets would have allowed AT&T to expand its LTE footprint to cover 97 percent of Americans. How AT&T will make up that difference isn’t yet known, but AT&T needs to act quickly, as Verizon has already blanketed some 190 markets and 200 million Americans with LTE. While AT&T was focused on winning regulatory approval for the takeover, rivals were negotiating their own airwave deals. As a result, several spectrum assets that would have still been available to AT&T are now off the table. Its remaining options are time-consuming, expensive and risky, says Cowen & Co. analyst Colby Synesael. AT&T can either seek to buy spectrum from another company, wait for the government to auction more frequencies or try to squeeze more capacity out of its current airwaves.