I think that interpersonal communication plays a vital role in Reitman's film. On one level, there is a clear communication between Adam and Emma in that they wish to only share sexual relations between each other and not engage in the more complex emotional realm. There is clear interpersonal communication here as both end up agreeing to this setup where there are "no strings attached." Certainly, one cannot fault them for poor communication. It is clear that both of them articulate their point of view thoroughly and precisely.
Where interpersonal communication becomes more pronounced is the emotional dynamic that emerges between them. To this extent, both of them rebuff and try to repel the growing emotional language that emerges in their relationship. Adam is shown to be willing to "crack" first in this configuration, only to see Emma do the same later on in the film. Adding to this is the subtext of how there is a lack of interpersonal connection between Adam's father and his girlfriend, Vanessa, cannot remain together because of her fear of "old people." In this, there is another example of how interpersonal communication is avoided in the short term, but inevitable in the wider frame of focus. The interpersonal communication between Adam and his father is a bit harsh, but does display how this relationship will withstand such challenges. With the ending in which everyone finds some level of happiness through the montage sequence, the audience is left to presume that interpersonal communication has taken place on some level with all of these different relationships. The more dark view is that the montage is actually a way to avoid the difficulties of interpersonal communication, rather showing clips and montage footage to superseded the challenges of interpersonal communication. In this, the film ends traditionally, only to raise the idea that interpersonal communication is far from traditional, but rather unique and germane to every emotional situation that necessitates it.