To use the iPhone as a business customer, you must sign a 2-year service agreement, or a renew a 2-year service agreement, if you’re an existing AT&T cellular customer.
The plans are as follows:
$45/mo. 200 SMS. Unlimited Data. Visual Voicemail
$55/mo. 1500 SMS. Unlimited Data. Visual Voicemail
$65/mo. Unlimited SMS. Unlimited Data. Visual Voicemail
If your business requires you to travel internationally, there are Global Data Add-Ons for the iPhone that can be purchased for an extra charge.
$24.99/mo. 20MB Data Global Plan.
$59.99/mo. 50MB Data Global Plan.
Many websites speculate that this is a sign that MANY business software developers are prepping software for the iPhone; such as IBM releasing Lotus Notes for the iPhone.
The iPhone developer kit (called "The iPhone SDK") should yield some amazing implementations of both business and consumer applications.