Here's what you get when you dial special numbers from a public courtesy phone at the UW.
A number ending in x means that every (not otherwise listed) digit which was tried in the place of that x gave the result indicated. NC means that the call couldn't be completed, and warble is the crazy vacant-level tone we have here at the UW.
A number noted with ? just gives an empty line and thus deserves further investigation, as do all dialtones.
*11 - dialtone *12x - NC *13x - NC *14x - NC *15x - NC *168 - dialtone *16x - NC *172 - dialtone (apparently forward-all-calls on a PBX) *173 - dialtone *174 - dialtone *178 - dialtone *179 - dialtone *17x - NC *18x - NC *19x - NC *199 - dialtone *19x - NC *1*0 - dialtone *10 - dialtone *1# - NC *21 - dialtone *22 - dialtone *23 - dialtone *24 - dialtone *25 - dialtone *29 - warble *20 - dialtone *2x - NC *31 - warble *32 - warble *33 - dialtone *34 - dialtone *35 - dialtone *38 - dialtone *39 - warble *3*x - NC *421 - dialtone *42x - NC *43x - NC *44 - NC *45 - dialtone *46 - NC *471 - dialtone *472 - dialtone *473 - 3-stutter (here I stopped and skipped to *5) *52 - busy *53 - warble (flash-*53 parks a call) *54 - unpark elsewhere-parked call *56 - warble *57 - dialtone *58 - dialtone *59 - dialtone *50 - busy *5* - NC *5# - NC *65 - dialtone *66 - warble *67 - dialtone *68 - dialtone *6x - ? *70 - disable call waiting *71 - dialtone *73 - cancel do-not-disturb *74 - dialtone *75 - dialtone *751N[...]# - program speed dial slot N (unlimited digits, apparently) *76 - NC *77 - NC *78 - 3-stutter (turn off forwarding) *79 - enable forward all calls to voicemail *7# - NC *82 - dialtone *85 - dialtone *86 - busy *88 - dialtone *94 - dialtone *94 - dialtone *96 - warble **x - NC *#x - NC #1N - speed-dial slot N #2 - warble #3 - dialtone #312 - voicemail #310 - NC #31x - warble #329 - 3-stutter #32x - warble #333 - some voicemail #340 - Student Telephone Services #356 - dialtone (outside line) #366 - ? #369 - 3-stutter #377 - dialtone #379 - do-not-disturb (all calls to voicemail) #38x - NC #391 - ? #3911 - calls 911, surprisingly #399 - ANI #3xx - warble #3* - warble #30x - pager? #4x - NC #5 - warble #6xx - NC #7 - warble #8 - ? #9 - redial #*x - warble #030 - busy #091 - busy ## - ? #0xx - NC