Yes, you can sub soy for real milk in baking - 1:1 replacement ratio. Now, depending on the recipe, there will be some changes. For example, in bread that used milk and doesn't have any additional fat or sugars - the bread will not be as tender and will stale faster, the fat acts as a tenderizer and a moisture retainer, she sugar attracts moisture from the air to help keep it moist.
Soy also can cause things to brown more than milk.
Hope this helps some.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain