The French have strong feelings about politeness and often if a French person is "rude," he is simply reacting to a foreigner's affront to French etiquette. Knowing the rules can keep you from being an "Ugly American."
If you don't speak French, mention that and apologise. Many French people speak English but you should never assume that. Learn a few key phrases, such as "bonjour," "pardon" and "merci." They appreciate any effort.
If you are calling a French person, it is up to you to identify yourself as well as the person you are calling. Once you have confirmed that you have reached the right person, ask how he is first.
It is impolite to say, "I want to speak with Bob" or "Can you tell me if ...?" The French soften their questions so they come out as, "I would like to speak to Bob" or "I was wondering if you could tell me... ."
You can never use "please" too much. Even if you are just asking for the time, the French welcome a "s'il vous plait."
Loud talkers annoy people worldwide but many Americans don't realise that they speak louder than the French. Dial down your volume so as not to come across as yelling at the person you're calling and, if you're in public, passersby will thank you as well.