This can be done through either a Change Service order or a New Service order in the AT&T eOrder tool. These options are found on the left-hand side of the AT&T eOrder home page.

What is the easiest way to order a new AT&T Toll-Free MEGACOM number on an existing T1.5 circuit?
This can be done through either a Change Service order or a New Service order in the AT&T eOrder tool. These options are found on the left-hand side of the AT&T eOrder home page.