The correct answer is to use a TPM - Trusted Platform Module - for that key. Accessing the TPM itself requires a password, but the hardware prevents against bruteforce/dictionary attacks.
Does Apple iPhone uses mobile TPM? Any known mobile phone?
The iPhone does not, and I'm not aware of any that do. Even the Blackberry, which is intended for high security of such things, simply uses PBKDF2. However, a TPM is the best solution here.