We have used 802 routers for dial up over ISDN.Although this is not part of your original Q. When we initially set up the router we had nightmares configuring DDR. One of our clients had horrendous 'phone bills because the isdn line was being brought up by uninteresting traffic and routing table updates. Try and use static routes where possible, and be specific with access lists.
If you've already considered this then my apologies for waffling, if not it may save u a hefty 'phone bill.