Dear Prasanna,
Are you sure that calls are not even coming to AS?
In fact, maybe calls are coming trough PRI and then tries to dial telco again but telco is giving busy signal to those calls...
example:
1. someone dials PRI number 2720055 and he comes to the AS
2. num-exp or translation rule is applied and now AS dials telco number 160221,,,,1212121212
3. Telco gives busy signal
why?
1. number is really busy
2. number is invalid
3. pause time is not long enough
4. there are some user authentification which needs to be proccesed during a call
...
maybe you can try to debug and see if calls are coming to the AS and are they are going out of AS?
Regards,
Goran