The bidding war for Straight Path Communications heated up even further on Wednesday as a new high bid came in for the tiny holder of valuable wireless airwave rights.
AT&T thought it had a deal to buy Straight Path, which owns high frequency airwave licenses in the 39 GHz and 29 GHZ band, for $95.63 a share blast month. But a mystery bidder, rumored to be Verizon, has since entered the fray. On Wednesday, Straight Path disclosed that the mystery bidder had upped its offer to over $135 a share, constituting a superior offer, the company said.
But Wall Street clearly thinks there will be more action to come as Straight Path (STRP) stock shot up 22% to 153.34—well above the latest mystery offer that values the total company at $2.3 billion.
AT&T (T) and Verizon (VZ) had no immediate comment on Wednesday. Straight Path declined to comment beyond the disclosure of the superior bid.
AT&T has three days to make a better offer, Straight Path said. If the company terminates the agreed-upon deal with AT&T, however, it must pay AT&T $38 million.
Get Data Sheet, Fortune’s technology newsletter.
The airwave licenses that Straight Path owns are suitable for next-generation, super high-speed 5G wireless networks, which are slowly rolling out over the next few years. The next generation of wireless technology will be fast enough to allow downloads at 10 to 40 times the speed of current 4G LTE networks, suitable for virtual reality applications or transmitting masses of data from corporate connected machinery.
Straight Path owns spectrum licenses covering the entire country in the 39 GHz band and additional licenses for the 28 GHz band. Known as the millimeter bands, the higher frequencies are capable of carrying far more data than lower bands like the 700 MHz currently used in 4G wireless networks. But they have trouble traveling as far and penetrating obstacles. Verizon has already announced plans to conduct a variety of trials this year using the higher frequencies, as has AT&T.
The licenses owned by Straight Path have traveled a tumultuous journey. Telecommunications carrier IDT (IDT) bought the rights out of the bankruptcy of Winstar, a failed wireless service, back in 2001. Unable to extract much value from the licenses over the next decade, IDT spun off the rights with Straight Path in 2013.
Straight Path then faced an FCC investigation over whether it was putting the licenses to proper use. In a deal reached with the FCC in January, some of the licenses were revoked, and Straight Path agreed to pay the agency 20% of any sale.