Skype offers real-time voice translation services.

Skype has started offering real-time language translation for its voice calls, supporting more than 150 languages, in partnership with Voxeo and Language Line Services. The pay service costs $2.99 per minute. You can use the service whenever you want without much trouble -- you'll hear a translator an average of 45 seconds after making your request. Note that OSX users currently can't access the feature.