Hmm, I'm quite sceptical to this idea because the whole concept is hinged on the presumption that the individual who wants to change their speech patterns can hear the difference (or can be trained to hear the difference) between their own accent and other people's. I have found that, in many cases, people who have started learning a foreign language later in life cannot get rid of their accent primarily because they just can't identify differences in pronunciation, rhythm and intonation. Of course individual differences account for a lot, some people naturally have a good ear and an aptitude for imitating other accents, however these people wouldn't need accent modification training in the first place.