A lot of stand alone GPS unit's offered this ability, but I haven't seen it on any Android phone. The difference is that many GPS' actually use recordings of peoples voices reading the words frequently used in directions (e.g., turn right, feet, meters, "in 60 feet' etc. Android phones use speech synthesis. The information is stored simply as text, and when needed the phone converts the text to speech. This approach saves a huge amount of storage space, since text files require a lot less space than voice recordings.