I haven’t read it, and I’ve only read a snippet or two about N. S. Prabhu, mainly in the context of something called the Bangalore-Madras Communicational Teaching Project, which I think took place around 1979-1984. Because of my lack of knowledge, I don’t have any opinions about it one way or the other (except that it sounds intriguing); I just wanted to let people know that it’s here:
I can’t tell for sure, but it looks as if it’s the whole book. You need a PDF reader, such as Adobe or Foxit, to read it.
A word of caution: I’m not 100 percent sure about the copyright situation regarding Oxford University Press’s putting the book online, but in their legal notice they say that materials on their ELT website “may be retrieved and downloaded solely for personal use.” Their legal notice is here: oup.com/elt/site_info/privacy?cc=global