AT&T this week unveiled business plans for Apple's iPhone, the first time that the mobile carrier has courted corporate customers of the smart phone. But the lowest-cost data plan is still two-and-a-half times higher than a comparable consumer plan.

The news comes on the heels of reports - still unconfirmed - that IBM will soon add support for the iPhone to its Lotus Notes enterprise messaging system.

AT&T's new iPhone plans for businesses, which it spelled out on its site, come with a minimum two-year service agreement. Unlike its consumer iPhone plans, however, which combine voice and data into one fee, AT&T's business billing splits the two.

Enterprise data plans, for example, start at $45 monthly for 200 text messages, $55 a month for 1,500 text messages and $65 for unlimited texting. All three plans bundle unlimited domestic data access via AT&T's EDGE network. Consumer bills, in comparison, break out the 200-message data part of the lowest priced plan as just $20.

Businesses must also sign up for a new voice plan, or have an existing one in place, for each iPhone. Those voice plans are sold at standard corporate rates that range from $39.99 for 450 monthly minutes to $199.99 for 6,000 minutes monthly in plans without minute sharing among users.

AT&T is also offering a $25 monthly credit to new iPhone accounts activated by 31 March; the credit will be applied to bills through the end of 2008.

Last week, reports circulated that IBM would port Lotus Notes to the iPhone, but as of Monday, IBM had not made the speculation official with an announcement from its Lotusphere trade show now in progress in Orlando, Florida.

IBM is hosting a press conference today where it will, according to a spokesman, discuss "new functionality for Lotus Notes/Domino, including new Web 2.0 functionality." AT&T is the exclusive carrier for the iPhone in the US.