AT&T may be able to cut T-Mobile's $39 billion price tag, if the costs of concessions made to appease the Department of Justice rise above 20 percent of that price, or $7.8 billion.

The telecom giant is fighting for the merger, after the DOJ sued to block the acquisition last week. On Friday, we reported that AT&T may be willing to divest parts of the business, including spectrum and customers, to push the deal through, but would likely walk away from the deal if those concessions broke the $8 billion mark.

But Bloomberg reports that AT&T now might be willing to make more concessions, in exchange for a drop in the sale price. According to sources close to the deal, AT&T might be willing to divest up to $15 billion worth of T-Mobile and AT&T assets in order to complete the merger, which would make it the nation's largest wireless carrier.

However, the telecom giant would likely put the brakes on the deal if the concessions cross 40 percent of the deal price tag. AT&T would then be required to pay T-Mobile parent company Deutsche Telekom a $3 billion break-up fee, plus an estimated $3 billion in spectrum and roaming deals.

If the deal -- and concessions -- are approved, where would AT&T be willing to sacrifice spectrum?

Strategy Analytics, a Boston market research firm, analyzed the AT&T actions that could satisfy the Department of Justice and determined that AT&T would likely have to sell off spectrum in major markets such as Dallas, Seattle, Honolulu, Houston and Oklahoma City.

The firm estimates that this would result in a spectrum "fire sale" in which smaller operators, such as Sprint, MetroPCS, and US Cellular, could pick at this spectrum at discounted prices.

It estimates that AT&T will have to persuade Deutsche Telekom to waive its penalty clause, or extend the date beyond the original March 2012 deadline.

Both companies said they will challenge the DOJ lawsuit in court. AT&T has asked for an expedited hearing; the case could go to court within the next two months.