Care. Actually, really care. Treat them like they are your only or most important client.

Airlines and other crappy companies are lowering this bar but Zappos and other amazing companies are raising it.

Also - a good post from Seth on why "answering on the first ring" might be as important as delighting your customers in a more innovative way.

http://sethgodin.typepad.com/seths_blog/2006/03/waiting_in_line.html