Apple Corp. took a very troubling step this week in rejecting Google’s “Google Voice” software tool, effectively blocking the nifty application from use on Apple’s hugely popular iPhone.

So what is Google Voice and why is Apple’s rejection of the application so troubling?

Google Voice lets you route your work, home and wireless phones to a single number provided by the Internet search giant – and that’s just the start. It lets users make free local and cheap international calls. It generates transcripts of voicemail phone messages and drops them in you email inbox. Users can search those transcripts for words and names at the touch of a few buttons, and it gives users access to Google’s free directory assistance service.

Google Voice appeared to be tailor-made for tech savvy iPhone users, but Apple rejected an iPhone version of the software.

There is widespread speculation that Apple rejected Google Voice at the behest of its exclusive U.S. service provider for the iPhone, AT&T. And there’s little question why: Google Voice effectively gives away for free many of the services that AT&T makes a lot of money selling.

It’s safe to say that Apple would not have rejected Google Voice for the iPhone were it not for its exclusive service deal with AT&T.

Apple’s action points up once again the problem of “handset exclusivity” deals, those ubiquitous agreements by cell phone makers with wireless service providers that chain up consumers. Of the ten most popular handsets in the market in 2008, eight were shackled to a single wireless service provider such as AT&T or Verizon through exclusive deals.

Such exclusivity deals mean consumers who want to get virtually any of the most popular cell phones must first agree to use a certain wireless service provider.

These exclusive deals thwart competition, discourage innovation, and lead to higher prices. Exclusivity deals also create significant obstacles to consumers who would choose to switch wireless providers for lower rates or better service. In addition exclusivity arrangements are also a barrier to the entry for new competitors in the market for wireless devices.

And in the case of Apple, it was doubtless its exclusivity deal with AT&T forced the company’s rejection of Google Voice, robbing all iPhone customers of Google’s ingenious new software application.

The Federal Communications Commission has launched an investigation into whether handset exclusivity deals hurt consumers and the issue is getting increasing attention in Congress. Both are heartening developments.

Consumers Union, the publisher of this blog, believes it is long past time for these exclusivity deals to be outlawed. The only clear beneficiary are the big four U.S. wireless carriers – AT&T, Verizon, Sprint and T-Mobile – which already control more than 90 percent of the market.

There will undoubtedly be huge pressure exerted in Washington by the powerful wireless industry and the army of lobbyists it employs. We hope government officials and lawmakers will resist all that pressure and take the pro-consumer step of banning handset exclusivity deals.