I think you can with Best Buy. I'm looking at getting a SG 5 with Verizon from Best Buy online for like $1 with a contract renewal. I just hope they don't want to charge me for shipping.
Usually a few days before BF Walmart puts out their actual ad with the information next to each item as to whether or not they are in store only or online AND in store. The doorbusters are rarely online. The time they become available has changed the last few years. I have always done my WM shopping online mostly because I am after the non-doorbuster items.