Use asterisk to dial outbound number with extension

Sometimes, you want to reach an outbound number and when it answers, press some digits to naviguate through IVR.
The most common case where this can happens is when you want the callers from your PBX to reach a number and go direclty to a given extension. This prevents the caller to enters himself the extension number of the foreign side.
To make it done, you can use asterisk Dial option D.

D([called][:calling]) - Send the specified DTMF strings *after* the called
party has answered, but before the call gets bridged. The ‘called’
DTMF string is sent to the called party, and the ‘calling’ DTMF
string is sent to the calling party. Both parameters can be used
alone.

Situation : From your office, you want to have a “speed dial” extension (eg: 2025) that will allow users to reach the other office (eg: at phone number 5140000000) sales departement (eg: at extension 1234). So, instead of calling the phone number 5140000000 and then dialing 1234, your dialplan can look like :

exten => 2025,1,Noop(Caller ${CALLERID(all)} want to reach foreign office and extension 1234)
exten => 2025,n,Dial(dahdi/g0/5140000000,30,D(1234))
exten => 2025,n,Hangup

So, what will happen is, as soon as the foreign office system (at 5140000000) will answer, asterisk will “auto press” digits 1234 and then bridge the call to the caller.
You can also send digits to the caller channel.