in sip.conf

[<some random extension number like 1201 or whatever>] ;ipkall
type=peer
dtmfmode=rfc2833
context=fromipkall
insecure=very
host=voiper.ipkall.com
nat=no


in extensions.conf

[fromipkall]
exten => <extension you picked earlier>,1,SetCallerId("From WA Number" <${CALLERIDNUM}>)
exten => <extension you picked earlier>,2,Dial(${PHONE})