Call Without Pickup
From KlavoWiki
To call a telephone throught the inbuilt speakerphone so the person doe not have to pickup the phone to answer the call.
exten => 5555,1,SIPAddHeader(Call-Info:\;answer-after=0)
exten => 5555,n,Dial(SIP/201)
exten => 5555,n,HangUp
I have tested this with Linksys Phones. Trying the above on a Polycom phone will not work and does require addattional configuration.