I believe that ATM, even in its perhaps immature state, is useful and cost-effective in a number of applications today. In particular, the cost of wide-area DS-3 ATM services can be very attractive when compared to a number of point-to-point DS-3s.
TAANSTAFL. You keep forgetting that underneath ATM there are the same SONET or clearline DS-3s/OC-3s etc. So, just by using IP routers instead of ATM switches you get 30% more bandwidth for the same price. ATM does not appear to make economical sense when applied to both data and voice communications. So, from the point of view of a user purchasing something carriers offer ATM may make sense (if carrier does not offer native IP) -- but from the point of view of a carrier ATM does not look that attractive. You still have to run IP over ATM (there's no such thing as native ATM applications yet), and the extra level of encapsulation does not bring anything worth 30% of bandwidth. In terms of real switching capacity (i.e. user data payload) the new generation of IP routers is pretty much close to ATM switches -- and quite cheaper. --vadim