Busy in silence

I'm placing VoIP calls and I've noticed that few calls that are connected to ops are just plain silence. I've picked some of them and dialed through a land line and got a busy message (this phone number is busy at the moment .. blah blah).
I don't know if I missed a piece in the configuration for vicidial, asterisk.
should I blame the VoIP carrier?
I'm using VERSION: 2.2.0-215 BUILD: 90908-1207 and Asterisk 1.4.21.2
Rgds
I don't know if I missed a piece in the configuration for vicidial, asterisk.
should I blame the VoIP carrier?
I'm using VERSION: 2.2.0-215 BUILD: 90908-1207 and Asterisk 1.4.21.2
Rgds