A whole slew of research in the past thirty years has shown that primates can learn sign language and communicate with humans.
Here are some basic links for your surfing pleasure - I used them as a source for inspiration as I created Jerry.
The following links are maintained by external sources.
Here is the Official Washoe website:
Washoe is the most famous primate around - she has a several hundred word vocabulary!
Here is a general info-site:
An AP article on the subject: http://www.athensnewspapers.com/1997/112897/1128.a2orangutan.html
And finally, a list of current research projects involving primate enculturation: http://www.cwu.edu/~cwuchci/research.html