I'm thinking Max's shoe phone from "Get Smart" in 65, but there has to be one before that.
I thought of that too, started looking into battlefield communication, but then you get into what is a radio and what is a cell phone.Though ham radio guys probably used mountain top repeater sites or on top of tall buildings prior to that and could make phone calls as long as the were in range of the repeater. So I'm sure there was a product like that prior to cellular proper.
More likely an early hearing aid. The first ones had large speakers that you had to hold up to your ear.