[Asterisk-Users] Freak incidents, who's to blame?

[Ryan Courtnage]

Hello all,

Everyone has probably experienced this at some point in the past:
You pick up your analog phone.  Rather than hearing dialtone, you are  
connected with someone who has just called you.  Neither you nor them  
heard a ring.

Maybe it's just me, but it seems these "freak incidents" would occur  
more frequently years ago, than now.

I've now experienced this a couple of times with an * system (TDM400p  
- quad FXO):
A SIP exten dials digits which are answered by a Zap trunk.  As soon  
as Zap answers, the SIP extension is connected with an inbound (PSTN)  
caller (who was expecting to hear an IVR).

My questions are:  Who's to blame (telco, tdm card, * config,  
gremlins)?  Is this avoidable?

Thanks
Ryan