[root@voip asterisk]# vi extensions.conf

[general]

static=yes       ; These two lines prevent the command-line interface
writeprotect=yes ; from overwriting the config file. Leave them here.

[from-sip]

exten => 2048,1,Dial(SIP/2048,20)
exten => 2048,2,Voicemail(u2048)
exten => 2048,3,Hangup

exten => 2148,1,Dial(SIP/2148,20)
exten => 2148,2,Voicemail(u2148)
exten => 2148,3,Hangup

;voicemail
exten => 2999,1,VoicemailMain(${CALLERIDNUM})
exten => 2888,1,VoicemailMain(3043)