In general this should be fine. You
should use recent 12.2 code to get
some fixes regarding callback issues
with MPPP, where subsequent links
were not called back.
You can use ISDN/dialer callback (where
the initial call is NOT answered), or
PPP callback (where it is). Some URLs
that may help you:
http://www.cisco.com/warp/customer/793/access_dial/dialer-redial-callback-4686.html
http://www.cisco.com/warp/customer/793/access_dial/bri_isdn_callback.html
http://www.cisco.com/warp/customer/793/access_dial/isdn-ppp-callback.html
In your case, you would want to put all
the BRI's into a dialer rotary group.