Voice Guidance is available on MapQuest 4 Mobile iPhone app. It is a Feature that differentiates from other free navigation apps available for iPhone.
The new feature is that Voice-Guidance speaks and informs upcoming turns and Off-Route Assistance. It tells you when you’ve taken a wrong turn, and gives options to get back on track.
The file size of this update version 1.5.1 4.2 MB and is compatible with iPhone and iPod touch, requires iPhone OS 3.0 or later.