Ray, as mentioned in the previous post ATM is not being replaced, its just getting obsolete, due to various dynamics. As is the case is with any legacy technology when a new more viable and cost effective technology comes up.

If you see there are couple of legacy networks still using ATM, and most of the defence networks traditionally have had a ATM backbone. But now thats changing, in my experience have seen an organization going from ATM to MPLS and Carrier Class Ethernet Backbone.

From the certifications standpoint, you can consider CCIP to start with, CCNA is a prerequisite for the same. Once you are comfortable with the professional level certification (CCIP) you can progress towards the Expert Level CCIE (Service Provider).

Probably Martin here can advise you more on the Certifications and study courses.

HTH-Cheers,

Swaroop