Sorry, you threw me off with the 192.X.X.X number.
Let's start from the begining with more information.
Are you set up as a server-gateway with 2 NIC's or just a server with 1 NIC?
Are you trying to do nslookup on your internal private ip or your external public ip?
Are you behind a hardware firewall/router? This question can be a bit tricky because some "modems" (like the cisco 675's and others) can actually be set up as routers depending on your ISP.
Try ifconfig and see what your external ip address is. If it falls into one of the catagories below, then you have another peice of equipment masking your external ip address and nslookup won't work properly.
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
Does nslookup work with any other ip addresses?
Try nslookup 12.254.149.181 this should come back with client.attbi.com.