it totally depends on who you were voting for.
i voted always for the people i loved, which last year was clay. his line was always jammed, so i would get in one out of every four tries. this caused some to think the lines were down and "test" by calling another line and get through but that would just register a vote...
there was no limit. once i was dialing for four different people in one hour. after a while i began voting "strategically" - i.e. i knew clay and ruben would always get tons of votes, but i wanted to boot carmen off, so i'd start voting for say, trenyce like crazy.
its toll free, 1-866 numbers. if you get a busy signal, don't worry. the line does not tell you the name of who you dialed, but "thank you for voting for contestant number 3" so you better remember the numbers! i hit no max last year - i'd vote over and over and over.