looks like you might be able to use the following parameters to create a card with 0.0 balance among other things and bind the callerid to the card...
then have the user call back and enter the voucher now that they can be authenticated by the callerid that was previously bound to the card
Quote:
;
; enable the callerid authentication
; if this option is active the CC system will check the CID of caller
cid_enable = yes
if the callerID is captured on a2billing, this option will create automatically a new card and add the callerID to it
cid_auto_create_card = yes
; set the length of the card that will be auto create (ie, 10)
cid_auto_create_card_len = 10
; If cid_auto_create_card has been set to YES, the following options will define with which configuration we will create the card
;
; billing type of the new card
; ( value : POSTPAY or PREPAY)
cid_auto_create_card_typepaid = PREPAY
; amount of credit of the new card
cid_auto_create_card_credit = 0
; if postpay, define the credit limit for the card
cid_auto_create_card_credit_limit = 1000
; the tariffgroup to use for the new card (this is the ID that you can find on the admin web interface)
cid_auto_create_card_tariffgroup = 6
; enable the option to refill card with voucher in IVR (values : YES - NO)
ivr_voucher = yes
; if ivr_voucher is active, you can define a prefix for the voucher number to refill your card
; values : number - don't forget to change prepaid-refill_card_with_voucher audio accordingly
ivr_voucher_prefix = 8
if it works you create the card the first time you call the system and present your callerid and then use the successive call to recharge the card with the value of the voucher. this way you only have to distribute vouchers