Try this:
ppp callback
To enable a dialer interface that is not a data terminal ready (DTR) interface to function either as a callback client that requests callback or as a callback server that accepts callback requests, use the ppp callback interface configuration command.
ppp callback {accept | request}
Syntax Description: accept
Enables this dialer interface to accept PPP callback requests (and function as the PPP callback server).
request
Enables this dialer interface to request PPP callback (and function as the PPP callback client).