sip.conf

[20]
context=local
type=friend
;authentication
secret=oquidroid
;host = 192.168.43.1
username=oquidroid
callerid=oquidroid
host=dynamic

extension.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()