provided by Star2Billing S.L.

Using asterisk 1.6 a2billing 1.3.4.
I nailed it down.. and want to share my experience with the group..after spending almost a week.
The output in the CLI is very helpfull to diagnose.

IVR says the number is currently unvaialble..(not able to input numbers yet)
After fixing the default prefix in the calling card rate, ... it just says the number is busy.
In the CLI output saw that it was dialing ext 1000.. But how did it get this number ??? (no clue)
Anyhow it was trying to dial the 1000 extension where the callback came from automatically. It didn't make sens for a callback. I didn't even input a number yet..
The FIX:
The a2billing.php is configured for a web callback... not phone call back (CID callback)

Around the line 740
Change the setting for
$A2B->agiconfig['use_dnid'] =0;
// $A2B->agiconfig['use_dnid'] =1;
$A2B->agiconfig['say_balance_after_auth']=1;
// $A2B->agiconfig['say_balance_after_auth']=0
$A2B->agiconfig['cid_enable'] =1;
// $A2B->agiconfig['cid_enable'] =0;
$A2B->agiconfig['say_timetocall']=1;
// $A2B->agiconfig['say_timetocall']=0;

Also very important if using CID-CALLBACK..do not use HANGUP. Use a wait 60 so that it keeps the variable in memory.

In your callback context..
exten => _X.,n,AGI(a2billing.php,2,cid-callback)
exten => _X.,n,Wait(60) //Give time for the callback to call you back.

and then your normal context for callback (a2billing-callback)
exten => _X.,1,Answer // Answer the call with variable from last call -
exten => _X.,n,AGI(a2billing.php,1,callback)
exten => _X.,n,Hangup

See here.
Rather than patch the source, you can simply use a different agi-conf section in a2billing.conf to configure A2B differently for each purpose.
Interesting. Thanks for your feedback. I haven't been keeping up with the Asterisk repo so I have no idea what they've changed regarding DeadAGI/AGI. It sounds like they've tried to keep backwards compatibility, despite the invasive changes I'd previously heard were going to happen.

Many thanks patrolg. Your post solved my problem wiht extension 1000. Wish others on this forum were as helpful as you.