@seryozha - That is an interesting answer. I have never experienced such. On my 406v2, I have 4 incoming lines, routed to one extn for the reception. I must say either my PBX is misconfigured or my analog card has a problem.
1. There are times when NOT all lines are busy, but when I make a call, it gets silently dropped. That is how I can describe it, because my phone screen gets to idle, as if I did not dial out
2. My PBX does (I've never heard it) NOT give the 3 fast beeps as you say. I have several 6408D+ and 2420 deskphones.
Please tell me where I should check for the cause of the anomalies.
Thanks