It's probably best to get yourself some books. The online documentation for both Asterisk and FreeSWITCH is shit, the IRC channels are mostly useless unless you already know a lot and the configuration files are just plain weird (Asterisk uses ini-style files with embedded programming, FreeSWITCH's configuration format pretends to be XML (which it certainly isn't)). Asterisk also has severe performance problems and AFAIR has some extremely bad code.
The entire idea with Plivo (much like Twilio and Tropo) is to simplify i.e. let web developers build telephony apps without having to learn much about a telephony engine.
