Dial by name directory - search by voice

Is it possible to allow callers to search a dial by name directory by voice?  Or at least spell out the name using letters?  For example, if someone is searching for John Smith, could they say "Smith" or "S-M-I" and get matching names?  I'm trying to create a hands free experience for callers who get to an IVR that allows them to Dial by Name.

Thanks!