I actually have trouble telling which voice is supposed to be Clinton and which is supposed to be Trump, plus it doesn't even come close to sounding like an actual phone recording.
It's a stretch but not nearly as much of a stretch as people think.
I've been spreading more or less the same theory as a joke since late last year (or maybe January).
Incidentally, have you looked at the latest bunch of DNC hack leaks? IT's both more damning and more mundane that expected (as in there's a mountain of evidence that the DNC and the Clinton campaign were colluding since before she officially announced her run, but the actual stuff they were colluding on is mostly pretty mundane - the worst thing I've seen so far myself is that the Clinton foundation was sharing donor lists with the DNC). I don't expect there's anything in there that will surprise anyone who already already had the appropriate, healthy level of cynicism about the party system in general.
Actually, the best conspiracy theory I've heard is that Trump isn't a Clinton plant, but a Putin plant. The idea is that on election night, Russia will robocall all the polling places in heavy Republican districts with bomb threats. This would then in theory result in an obviously questionable Clinton win, instigating a civil war.