They should not be charged.
The caveat is if it's an automated phone system you dialed (e.g. company) and they "answer" according to the phone service, but continue "ringing" on their side as it decides how to route you [think of it as the additional ring(s) you hear when you get transferred within the automated phone system]. Those are generally few and far between though.
Just popping in to say I agree. You shouldn't be charged unless the call actual connects. The automated system scenario is a good example of being charged for the call that a person doesn't answer. Hope this helps.
Really good question. In the past, it was common for some phone systems to assume that after a certain time ringing, the distant party had answered. This generally went away with the advent of more advanced signaling but when making international calls the system may be forced to fall back to the old way of doing things. Are you calling a 1st-world country like France or Germany or some place less developed.