Numbers for the three big US operators that carry the iPhone (T-Mobile, which didn't in Q1, hasn't released the Q1 numbers yet). iPhone was 57% of smartphone activations and 49% of ALL contract phone sales. Smartphones are 86% of contract sales.
To be strictly precise, these numbers are a mix of 'activations' and 'sales', which are not always consistently reported. The main delta is in second-hand sales. However, these do not (yet) appear to be big enough to change these numbers much.