Adam Philips, "Elephant Study Reveals Social Bonds, Communication Skills", VOA 8/29/2011:
Shermin de Silva, who finished her PhD in biology at Penn last year and is now the director of the Uda Walawe Elephant Research Project at Udawalawe National Park, Sri Lanka, is featured in this slide show explaining some of her research:
You can read her dissertation here: "Socioecology, acoustic communication and demography of Asian elephants in Sri Lanka".
And a couple of relevant recent papers:
Shermin de Silva, "Acoustic communication in the Asian elephant, Elephas maximus maximus", Behaviour 147(7), 2010.
Existing knowledge of acoustic communication in elephants is based primarily on African species (Loxodonta africana and Loxodonta cyclotis). There has been comparatively less study of communication in Asian elephants (Elephas maximus). In order to provide a basis for understanding the evolution and function of acoustic communication in proboscideans, I present a quantitative description of vocal communication in wild Asian elephants. I classify calls by acoustic features into 8 'single' calls, 5 'combination' calls and one possibly unique male call for a total of at least 14 distinct call types. Some of these vocalizations have never before been described. Certain low-frequency calls are individually distinct. Acoustic signals occur in a wide range of social contexts, with some differences in call production among age and sex classes.
Shermin de Silva, Ashoka DG Ranjeewa, and Sergey Kryazhimskiy, "The dynamics of social networks among female Asian elephants", BMC Ecology 2011.