Callback can be enabled in much the same way as it in the Cisco configuration itself. Instead of giving the callback, callback-line and callback-rotary attributes in the username statement, they are defined as AV pairs in the service=exec (for callback after getting to the exec prompt) or service=ppp protocol=lcp (for callback after PPP has been started) section in the daemon configuration.
For these attributes to be transmitted, exec authorization as enabled by "aaa authorization network TACACS+" or network authorization, respectively, is required.
Callback control via TACACS+ for ISDN interfaces is not currently supported.