As of recent data, approximately 85-90% of Americans who own mobile phones have smartphones. Therefore, if 95% of Americans carry a mobile phone, it is reasonable to estimate that a substantial majority of those phones are smartphones.
Given the options provided, "more than 3/4" seems to be the best answer, as it aligns with the high percentage of smartphones among mobile phone users.
So, the best response is: more than 3/4.