Recently, there was an entry in linguaphiles about the different pronunciations of "have" and "has" - with [v] and [z] when they're an auxiliary or full verb in general, but with [f] and [s] when they're in the "have to/has to" construction indicating necessity. (Compare with "used" which has [z] as the past tense of "to use" but [s] in the construction "used to" indicating former habit.)
People commented on the fact that "have" is not always pronounced [f] when followed by "to", but only when the necessity meaning is intended, and entangledbank (whom I always enjoy reading from) produced a minimal pair:
You can make a minimal pair contrasting the meanings of 'have' and 'have to':
the three books I have to read
With [hæftə] it means I must read them; with [hæv tə] it means I have them so I could read them if I wanted.
Clever! Me likey.