That's equivalent to a year of average monthly wireless bills, says research firm Harris International, which conducted the survey on behalf of Brightroam, a provider of products meant to help firms reduce international mobile phone roaming costs.

Roughly 15 percent of the U.S. global workforce travels overseas at least once a year, so businesses with more than 10,000 employees are currently shelling out upwards of $1 million for international cellular roaming annually, according to Brightroam.

"Wireless expenses are raging out of control for enterprises," said Joe Basili, vice president of research with the Association of Telecom Management Professionals (AOTMP), in a statement. "Telecom expense management is an issue that is rising to the forefront for most organizations and it's their number one priority for 2008."

The study was conducted online between November 28, 2007 and December 27, 2007, and it included responses from 830 respondents who had previously agreed to participate in Harris International studies. Of those respondents 212 were telecom decision makers and 618 were business travelers.

Additional study findings included:

• Eighty-nine percent of respondents think international roaming costs are too expensive, but only 39 percent have plans to switch to an alternative service provider.
  
• Roughly one third of the telecom decision makers who participated in the study said their employees expense international roaming charges instead of using some form of centralized billing system.
  
• Cellular coverage, call quality, airtime rates and convenience are the top four factors enterprises consider when choosing a roaming service provider.
  
• European countries are currently the most popular destination for business travelers (52 percent) followed by Asian countries (16 percent).
  
• Eighty percent of respondents said cell phones or smartphones are the most commonly used communications tool for their employees who travel overseas, and 57 percent of all calls placed during these trips are made using such devices.
  
• Half of all calls made by U.S. business travelers overseas are calls back to the States. And roughly two-fifths of the remaining calls are to other destinations within the same country.