SendDTMF - can not hear tone

Hello,

I am trying to use SendDTMF , but when I call the number, I can not hear the tone.

What I am trying to accomplish is the following;
Someone calls me through a toll-free calling service. The service waits for you to say “Hello”, and then has the automated response; “Press 0 to accept the call”. I want to send the “0” DTMF tone to accept and then route the caller into DISA (after a password).

When testing, I cannot hear the tone…

Here is my extensions.conf;

[voipms-inbound]
exten => _X.,1,Answer
exten => _X.,2,Wait(1)
exten => _X.,3,Background(hello-world)
exten => _X.,4,Wait(3)
exten => _X.,5,SendDTMF(0)
exten => _X.,6,Wait(5)
exten => _X.,7,Authenticate(1234)
exten => _X.,8,DISA(no-password,voipms-outbound)

(the version)
sadegs-desktop*CLI> core show version
Asterisk 1.6.0-beta4 built by sadegs @ sadegs-desktop on a i686 running Linux on 2008-03-10 03:41:46 UTC

(what happens when I call)
sadegs-desktop*CLI>
== Using SIP RTP CoS mark 5
– Executing [number@mycontext:1] Answer(“SIP/101117_asterisk-b6f06378”, “”) in new stack
– Executing [number@mycontext:2] Wait(“SIP/101117_asterisk-b6f06378”, “1”) in new stack
– Executing [number@mycontext:3] BackGround(“SIP/101117_asterisk-b6f06378”, “hello-world”) in new stack
– <SIP/101117_asterisk-b6f06378> Playing ‘hello-world.gsm’ (language ‘en’)
– Executing [number@mycontext:4] Wait(“SIP/101117_asterisk-b6f06378”, “3”) in new stack
– Executing [number@mycontext:5] SendDTMF(“SIP/101117_asterisk-b6f06378”, “0”) in new stack
– Executing [number@mycontext:6] Wait(“SIP/101117_asterisk-b6f06378”, “5”) in new stack
– Executing [number@mycontext:7] Authenticate(“SIP/101117_asterisk-b6f06378”, “5665”) in new stack
– <SIP/101117_asterisk-b6f06378> Playing ‘agent-pass.gsm’ (language ‘en’)
– <SIP/101117_asterisk-b6f06378> Playing ‘auth-thankyou.gsm’ (language ‘en’)
– Executing [number@mycontext:8] DISA(“SIP/101117_asterisk-b6f06378”, “no-password,voipms-outbound”) in new stack

Any suggestions?
thanks