The global voice and data roaming charges users incur when they travel internationally have long been a thorn in the side of multinational companies. Usage for data is particularly difficult to control for several reasons, one of which is that some of the usage gets sucked up by background housekeeping duties - such as regular automatic checks to weather, e-mail and other services. Even if there's no new data downloaded, these pings eat up some portion of the allotted kilobytes.

AT&T, the Apple iPhone’s sole carrier in the U.S., has global data packages that can cost multinationals up to nearly 2 cents per kilobyte in overage charges, depending on the country. Given that so much of future smart phone usage will be for data and multimedia, can enterprises use their devices globally without quaking in fear of the ultimate tab?

It’s unlikely that the worldwide mobile operators will find incentive anytime soon to lower their highly profitable roaming rates, according to Bill Bunavage, director of new business development at The Hastings Group, one of a group of 45 companies that have partnered to negotiate leveraged contracts with AT&T, Verizon and Sprint.

“The global roaming rates are just pure pass-through” by U.S. mobile operators from the various incumbent telecom operators in other countries, he explains.

However, a couple of recent developments could brighten the outlook. First, AT&T indicated in a press release last month that it would offer a no-contract-required iPhone 3G option “in the future.” This bodes well for the eventual sanctioned use of unlocked iPhones in which you can pop local SIM cards to get in-country rates—something previously not kosher with AT&T and Apple.

Meanwhile, a start-up called DeFi Mobile wants to make things even simpler. It expects to start marketing a carrier-grade service next month to the “mobile user who needs an alternative to a cellular channel,” such as “the international business traveler racking up large phone bills,” says company CEO Jeff Rice.

Rice says the company intends to use Wi-Fi to “solve the unpredictability of [both voice and data] roaming charges” and has “negotiated carrier-to-carrier deals with the majority of hot spots in the world.”

An enterprise buys access to a portal that allows its users to dial anywhere in the world from a Wi-Fi network for voice and data access. Connections are routed over DeFi’s own carrier-grade network to peering partner networks.

Joanie Wexler is an independent networking technology writer/editor in Silicon Valley.