Port in inbound calls + voicemail
The craziest part of this is the workaround for a serious bug in Bandwidth's
HTTP voice API (which they may yet fix, still negotiating with them about that).
When a call comes in, every 10 seconds that it is not "answered" the inbound
call gets cancelled by their upstream peer and then get retried. The caller
sees only one oubound call for this, so it doesn't look odd to them, but to us
it looks like they keep hanging up and trying again every 10 seconds. So what
we do for now is we wait 2 seconds after they disconnect before we decide
they're really gone. If they call back in those 2 seconds we just connect the
eventual bridge or voicemail to this new call and everything works out.