sip.conf
[20];numeric device name
context=local;route calls to the local context
type=friend ;can receive and make calls
secret=oquidroid
username = oquidroid;call extension 20 to get to the droid
callerid = oquidroid
host=dynamic

extensions.conf

[local]
;local clients have extensions from 10-99,
;write one general dialplan for all of them using pattern matching
exten => _ZX,1, Dial(SIP/${EXTEN},30)
        same=>n,Playback(vm-nobodyavail)
        same=>n,Hangup()