css background-size wont wrok for iphone?

I have this code:

background: url("../images/step1.gif") no-repeat top right/contain content-box;

but it wont work on iphone (I have iOS 4.3, I dont know about later versions) since no background is displayed at all. Do I need to change the syntax or is it just that the background-size property is not possible at all?

Thank you.