Mine

[root@aries mohmp3]# cat /etc/asterisk/extensions.conf
[general]
static=yes
writeprotect=no
autofallthrough=no
clearglobalvars=no
priorityjumping=no

[internal]
; Extension class for local users dialplan

;; FOR GETTING VOICEMAIL
exten => 200,1,VoicemailMain
;; FOR GETTING MAIN MENU
;exten => 7777,1,Goto(SIP/8006170141,1)

;; FOR CALLING OUT
; Set your CallerID to 8006170141
exten => _1NXXNXXXXXX,1,Set(CallerID(num)=8006170141)
; Dial your call out Asterlink via SIP
exten => _1NXXNXXXXXX,2,Dial(SIP/${EXTEN}@asterlink)
; Call not possible? Busy tone
exten => _1NXXNXXXXXX,99,Congestion

[incoming]
; Put your extensions stuff here
; Playback a asound: exten => <10 digit number>,<order number>,Background(filename with no extension)

; IVR BASICS:
; exten => <number pressed>,<order number>,<command>
; eg. exten => 1,1,Playback(you-reached-sales-office & bla)
;     exten => 1,2,Dial(SIP/sales-phone)
;     exten => 8006170141,2,Voicemail(u200)

; Ring SIP extension 200 for 30 seconds on Music on Hold
exten => 8006170141,1,Wait(6)
exten => 8006170141,2,Background(hello-and-thank-you-host41-please-hold)
exten => 8006170141,3,Goto(1,1)
; IRV for ext 1
exten => 1,1,Dial(SIP/200,30|m)
exten => 1,2,Voicemail(u200)
exten => 1,3,Hangup
; Random Funnies
;exten => 8006170141,1,Wait(5)
;exten => 8006170141,2,Background(carried-away-by-monkeys)
;exten => 8006170141,3,Background(lots-o-monkeys)
;exten => 8006170141,4,Hangup