Does the iTunes Store for iPhone, iPad, and iPod touch work over a cellular data network?
For all types of available content, the iTunes Store for iPhone, iPad, and iPod touch works over Wi-Fi. If you own an iPhone or an iPad Wi-Fi + 3G, you can also use a cellular data network (a 3G network is recommended for cellular downloads). Cellular downloads are limited to a file size of 20 MB or smaller, depending on the wireless carrier.