Apple's iPhone officially entered the corporate world in the United States this week when AT&T announced Enterprise Data Plans available to "corporate responsibility users" with an eligible voice plan. Previously, iPhone service was available only to individual users, who had to register with AT&T using a personal Social Security number.

Monthly data plans for enterprise iPhone users (which includes corporate, government, and educational institutions) start at $45, and include unlimited domestic data, 200 SMS messages, and visual voicemail, like the lowest-priced personal plan. (By comparison, the lowest-priced personal iPhone data plan costs $20 on top of an existing voice plan.) Data plans with 1,500 SMS messages per month and unlimited SMS messages cost $55 and $65, respectively. These rates don't include the monthly cost of the voice plan, which varies widely and is dependent on volume discounts and other enterprise service policies.

Global data plans are available for those who travel outside the United States; a 20 MB data plan is available for $24.99 per month, and a 50 MB data plan is available for $59.99 per month, offering service in 29 countries. (iPhone users have discovered that leaving their phones operating while traveling overseas without such plans can rack up enormous charges.) Enterprise customers must sign up for a new two-year service agreement, or renew their service agreement for two years, in order to be eligible for the iPhone enterprise data plans.

Early enterprise adopters stand to save quite a bit of money; AT&T is offering a $25 per month credit (which will appear on monthly invoices) through the end of 2008 for qualifying users who activate an iPhone Enterprise Data Plan by 31-Mar-08.