Well your wait is over. Dictionary.com is offering FREE apps for your iPhone. Yes, it is free compare to Mirriam Webster Dictionary that offer the same service for $24.95.
"The app let you easily access spelled words, alphabetical indexing, synonyms exampel sentences, non-standard uses, word origin and history. Another cool feature of the app is the ability to access definitions and synonyms offline. You can also hear pronunciations of words. The app store currently features ten dictionary apps." (2009, TechCrunch.com)
This will be in addition of my own personal iPhone free apps e.g. Translator, Skype and Holy Bible, all of them are for FREE. Check them out.