il te faut spécifier le numéro du channel et non d'un groupe dans la commande dial:

/*
> * data is ---v
> * Dial(DAHDI/pseudo[/extension])
> * Dial(DAHDI/<channel#>[c|r<cadance#>|d][/extension])
> * Dial(DAHDI/(g|G|r|R)<group#(0-63)>[c|r<cadance#>|d][/extension])
> *
> * g - channel group allocation search forward
> * G - channel group allocation search backward
> * r - channel group allocation round robin search forward
> * R - channel group allocation round robin search backward
> *
> * c - Wait for DTMF digit to confirm answer
> * r<cadance#> - Set distintive ring cadance number
> * d - Force bearer capability for ISDN/SS7 call to digital.
> */