If there are any problems with the cu dial-out process, you may want to use the -d option to cu to instruct the system to print diagnostic messages to your system console and the -l option to connect directly to the modem (if you added the "Direct" statement in the Devices file).
To test the modem connection on port 2, type
cu -d -lttyd2
Connected message should display on the console. Type AT and the OK message should display. If not, the modem is not correctly configured or there is a problem with the cable.
Connected does not display, check the debugging messages to determine where the connection failed.
Additionally, double-check that all your hardware connections are secure and that you are using a Silicon Graphics modem cable or one made to the specifications described in your Owner's Guide.