Sound of words app for iPhone and iPad
Sound of words is a free English phonological dictionary of over 130,000 words.
If you know how to write a word but not how to pronounce it, you can do a classic search and listen to its pronunciation.
If you know how to pronounce a word but not how to write it, you can search by phoneme and get its spelling.
The phoneme keyboard is available in both IPA and ARPABET standards.