The 16GB version of the Samsung Galaxy S4 is now available to pre-order on the AT&T website, both in the White Frost and Black Mist color schemes for $199.99 on a two-year contract. A SIM-free version will set consumers back a hefty $639, however. AT&T has yet to make an official announcment; perhaps to avoid an overload of pre-orders, given that we’ve already experienced some problems trying to access the webpage and complete an order. The 32GB version is also unavailable at this point. The US carrier will be shipping all Galaxy S4 pre-orders by April 30, arriving on consumer doorsteps shortly afterwards. It’s a short gap between the launch of the HTC One, which is launching on April 19 for $199.99 as the standard 32GB model and $299.99 for the 64GB variant.