We’ve never really had an AT&T business plan, but “Exclusively Business”:http://www.wireless.att.com/businesscenter/business-programs/small/programs/exclusively-business-faq.jsp actually seems like a pretty good deal. If you have 5 or more users, then you get an 8% discount on voice and data plans priced $35 and higher. Also, you can have corporate users direct billed (they are called Corporate Responsibility Users, is that a 1984 term or what!). They also wave the $36 per line activation fee.
The rumor is that the new iPhone will qualify for these, so now’s a good time to sign up. There is also a portal you can use.