"Back in the day" Steve Wozniak used his blue-box to call The Vatican, and was almost able to talk to the Pope by doing an impersonation of Henry Kissinger. So there's some history behind pranks like this.
"Anything that good hackers would find interesting / that gratifies one's intellectual curiosity."
Having read and enjoyed the Kevin Mitnick books, and based on the fact the target is extraordinarily high profile, I thought the social engineering side was interesting and others may feel the same.
It's a hack. I have no idea how to find David Cameron's offices number, and is a fairly good piece of social engineering reminding us that the old school still has some fight left.
As for the security review - this is just to cover them in case someone puts the .wav file online.
I think it's slightly interesting in context of Cameron's recent comments against secure crypto and increasing surveillance. Surveillance can't prevent pretexting attacks like this, nor did crypto enable the perpetrator to carry out the attack.
