You can call back PPP clients that dial in to asynchronous interfaces. You can enable callback to the following two types of PPP clients:
Clients that implement PPP callback per RFC 1570 (as an LCP negotiated extension).
Clients that do not negotiate callback but can put themselves in answer-mode, whereby a callback from the router is accepted.
The below link describes how to enable callback
http://www.cisco.com/en/US/docs/ios/12_0/dial/configuration/guide/dcascall.html