WordNet (r) 3.0 (2006):

hang up
    v 1: put a telephone receiver back in its cradle
    2: cause to be hanging or suspended; "Hang that picture on the
       wall" [syn: hang, hang up]
    3: interrupt a telephone conversation

Moby Thesaurus II by Grady Ward, 1.0:

151 Moby Thesaurus words for "hang up":
   adjourn, afterthought, bind, block, blockade, blockage, blow up,
   bog down, bottleneck, bureaucratic delay, buzz, call, call up,
   catch, come to nothing, complex, compulsion, continue, cordon,
   curtain, decelerate, defer, delay, delayage, delayed reaction,
   detain, detention, determent, deterrent, dial, difficulty,
   double take, drag out, dragging, drawback, explode, extend,
   fail miserably, fascination, fasten up, fixation, fixed idea,
   fizz out, fizzle, fizzle out, get nowhere, give a ring, go phut,
   halt, hang, hang fire, hazard, hindrance, hitch, hold off,
   hold over, hold the phone, hold up, holdup, hurdle, hypercathexis,
   idee fixe, interim, irresistible impulse, jam, joker, lag, lagging,
   lay aside, lay by, lay over, listen in, logjam, make a call, mire,
   misfire, monomania, moratorium, morbid drive, objection, obsession,
   obsessive compulsion, obstacle, obstruction, obstructive,
   one small difficulty, paperasserie, pause, phone, pigeonhole,
   poop out, possession, postpone, preoccupation, prepossession,
   prolong, prorogate, prorogue, protract, push aside, put aside,
   put off, put on ice, put up, recess, red tape, red-tapeism,
   red-tapery, reprieve, reserve, respite, retard, retardance,
   retardation, ring, ring off, ring up, rub, ruling passion,
   set aside, set back, set by, shelve, shift off, slacken, sleep on,
   sling, slow down, slow-up, slowdown, slowness, snag, stand over,
   stave off, stay, stay of execution, stop, stoppage, stretch out,
   stumbling block, stumbling stone, suspend, suspension, table,
   take a recess, telephone, tic, tie-up, time lag, wait, waive