The parody works on two levels. First, the AT&T ad is being recontextualized by taking the normal setting for cell phone use and putting it into an absurd world of spaceships and Star Wars characters. AT&T itself plays the role of the "evil empire," or "dark side" from the Star Wars films. It is also important to note that, as a non-profit consumer advocacy organization, NMR's work is noncommercial, and doesn't somehow replace or harm the market for AT&T's commercials. NMR also in no way competes with AT&T for telecommunications customers.
The video also parodies the Star Wars world created by George Lucas by portraying the serious and complex figure of Darth Vader as an ambivalent and shallow boss concerned about the service of his cell phone. Again the video is a noncommercial parody. The clips and sounds from the Star Wars movies are used in a new context and do not even nearly begin to replace the market for the Star Wars films.