ATM support for Linux is currently in pre-alpha stage. There is an experimental release, which supports raw ATM connections (PVCs and SVCs), IP over ATM, LAN emulation, MPOA, Arequipa, and some other goodies.
You can find everything there is to know on the following pages:
There is also a mailing list about ATM on Linux. You can subscribe to it on http://lists.sourceforge.net/lists/listinfo/linux-atm-general.
To unsubscribe from the list, please go also to the page above.
The mailing list is archived at http://www.geocrawler.com/lists/3/SourceForge/6487/0/.
The old ATM on Linux home page can be found at http://lrcwww.epfl.ch/linux-atm/.