The race to be the most “open” wireless carrier is heating up. On Wednesday, Verizon (VZ) will release a set of technical specifications that will enable non-Verizon branded cell phones to work on its network for the first time. Not to be outdone, early Tuesday AT&T (T) unveiled a new website which includes resources for consumers who want to use phones they’ve purchased outside of the carrier’s stores on its network.

Unlike Internet service providers — which are required to allow any laptop, browser or website to run on their networks — most U.S. carriers have historically blocked devices or applications that aren’t directly distributed by them. But more recently, U.S. mobile operators have adopted an “if you can’t beat them, join them” attitude.

Google (GOOG) takes at least some of the credit for the shift.

After it began lobbying for more open networks last year and launched its Android open mobile platform for developers, “AT&T and Verizon started to fight over which one seemed more open,” said Rich Miner, Google’s VP of mobile, at a recent conference.

But Verizon’s decision to open up was also a preemptive response to a government push for giving consumers more control over how they use their cell phones. The carrier’s announcement was strategically timed ahead of the Federal Communications Commission’s high-profile spectrum auction, which set aside a valuable portion of airwaves to be used for a new, open network. Verizon is believed to be the most likely winner of that block of spectrum, though we won’t know for sure until the auction closes — probably sometime in the next few days.

“Verizon Wireless’ Open Development initiative is driven by the company’s desire to encourage innovation, give customers new wireless choices, and quickly address opportunities to expand the wireless market,” the company said in a recent statement. Its open network will be available by end of 2008.

AT&T, of course, maintains that it will win the race.

“The driving force of our business is our commitment to be open to innovation and to offer our customers more choices than any other wireless company,” Ralph de la Vega, president and CEO of the company’s wireless unit, said in a statement.

But critics are skeptical that either carrier will become truly open, making it both simple and affordable for consumers to use outside devices and easy for developers to meet the specifications for getting their applications up and running on the networks.