.featuretext_middle responsive question

I would like to make my 4 featuretext boxes display one after the other on small portrait devices. I thought the following code might do it but it doesn’t at least not on my HTC. I might have to revert to 3 boxes. Thanks.

@media only screen and (max-width: 480px) {
	.span_4_of_4 {
		width: 100%;
	}
	.span_3_of_4 {
		width: 100%;
	}
	.span_2_of_4 {
		width: 100%;
	}
	.span_1_of_4 {
		width: 100%;
	}
}