On the Topic of Perspective...

 I'd rather not be hasty in trying to analyze Shamsie's motives in dividing the sections of the book into separate perspectives, but I think that sufficient information has been given to at least posit a decent guess.

To start hypothesizing the intent of multiple perspectives, we have to first analyze the effects it had on the reader.  At times, the shifting perspectives was somewhat disorienting, not aided by the quick skips in time within each section. There were many parts in the story where I had to go back to previous sections to see how the narration changed how certain characters were represented. The unfortunate portion of analyzing confusion partway through a story is that you can't truly be certain if it is a lack of reading comprehension or a series of plot points to be concluded later in the story; however, for the purposes of this analysis, I will assume that the confusion is an intentional aspect of Shamsie's story.

So, if there is a overarching plot point to be concluded with the final sections of this story, then that's the final answer? No, that is the purpose of the different perspectives narratively, but the confusion in and of itself has a purpose: to show the reader how different outlooks produce a vastly different world. This is evident by the style of the narration in each section: Isma's is verbose and conflicted, Eamann's is methodical then simplistic as he progresses his relationship with Aneeka, and Parvaiz's is uncertain and malleable as his role models shift. 

Overall, the contrasts between the perspectives grants further insight into the world that Shamsie is trying to portray, and the parallels show how each experience can be used to display empathy for one another. To delve into this subject for a moment, Isma has to feign conformity towards British ideals in order to survive in America and not be designated a dangerous individual, whereas Parvaiz has to feign conformity towards extremist Islam ideals in order to not be labeled a traitor and executed. The two are at complete odds with each other, yet taking a step back shows how they have much more in common than their ostracized positions indicate.

The reason that Shamsie placed the stories in the specific order she did was likely to cause the aforementioned disorientation. She reveals the motivations of characters in an order that allows the reader to question the events and beliefs of all parties involved, which should promote introspection and further contemplation concerning the deeper themes.