Something

------------------- sip.conf

[general]
port = 5060
bindaddr = 0.0.0.0
context = others

register => 111:senhafoda@gatecontrol.net/111

[2000]
type=friend
context=my-phones
secret=1234
host=dynamic

[2001]
type=friend
context=my-phones
secret=1234
host=dynamic

[ext-sip-account]
type=friend
context=from-voip-provider
username=111
fromuser=111
secret=senhafoda
host=gatecontrol.net
fromdomain=gatecontrol.net
quality=yes
insecure=very
nat=yes

---------------- extensions.conf

[others]

[my-phones]
;exten => 2000,1,Dial(SIP/2000)
;exten => 2001,1,Dial(SIP/2001)

exten => 2000,1,Dial(SIP/2000,20)
exten => 2000,2,VoiceMail(2000,u)

exten => 2001,1,Dial(SIP/2001,20)
exten => 2001,2,VoiceMail(2001,u)

exten => 2999,1,VoiceMailMain(${CALLERID(num)},s)

exten => _0[1-9].,1,Dial(SIP/${EXTEN}@ext-sip-account)