[Asterisk-Users] RE: Asterisk-Users Digest, Vol 15, Issue 85

[Rich Adamson]

> Does anyone know why you must sometimes dial a number twice to get it to
> connect?  We have IP phones and a TDM400P Digium card that connect to 2 PSTN
> lines.  Some numbers work fine and then other don't.
> 
> What gives?

The most frequent cause that I've heard of is that asterisk starts pumping
out the dialed digits too soon, and the central office equipment only 
catches the last seven of eight digits, etc.

Try inserting a "w" in the Dial statement something like this:
 exten => _21XXXXX,1,Dial(Zap/g1/w${EXTEN})

You won't find that documented very well in 'show application dial', but
the "w" injects something like a 250 millisecond delay before dialing.
You can use multiples if needed ("www") for a longer delay.