Remove the leading 0109# , and leave it only before the ${EXTEN}, like this. I have put prefix 9, you can use whatever you normally used. If it is for sify , you have to add a 00 also as the number for say USA has to go out as 0109#001NXXNXXXXXX. Hope it helps.
; dial an 800 outbound number
exten => _9800NXXXXXX,1,AGI(
agi://127.0.0.1:4577/call_log)
exten => _9800NXXXXXX,2,Dial(${TRUNK}/0109#00${EXTEN:1},,tTo)
exten => _9800NXXXXXX,3,Hangup
Regards
devafree