This is often a problem where a university has several modem lines and several thousand students trying to use them...
Make an entry for your university in /etc/remote (see remote(5)) and use <\@> for the pn capability:
big-university:\ :pn=\@:tc=dialout dialout:\ :dv=/dev/cuaa3:br#9600:at=courier:du:pa=none:
Then, list the phone numbers for the university in /etc/phones (see phones(5)):
big-university 5551111 big-university 5551112 big-university 5551113 big-university 5551114
tip(1) will try each one in the listed order, then give up. If you want to keep retrying, run tip(1) in a while loop.