As long as Asterisk is being used in a business setting and your have administrative prilidge over Asterisk and everything it's connected to, yes Server Fault would be appropriate.
The main difference between SF and the others like SU and Unix.SE is that SF requires you to be a System Administrator (et al) and the Question be related to your professional capacity (your job). The other sites are for enthusiasts or anyone who can put a coherent question together. All of them have a FAQ; please take a moment to at least breeze through the first section of each; we spent quite a bit of time trying to perfect ours.
The main reason for this separation is that the relatively few people who really know their stuff get very tired of the millions of inquisitive idiots (that might be a harsh term, but it's well earned historically). There's little guarantee that you'll get a correct or quality answer on SU or Unix.SE (the latter tends to be better because of the limited focus). I'd like to think SF has higher quality on account of the limited scope and limited audience (which I have generally found to be true).