Recently I found a google hit , that ask the question , Can we have ATO Model in Sales Order Without BOM.
Answer is NO , NOT at all.
BOM(Bill of material) is the place where we built the structure of our Model like
Finished goods etc
In case someone want to create a Sales Order for Model and don't want to Generate the Work order in WIP (Reason - Configuration already exists) , in that case they have to look for BOM profile options that look for the existing Stock before creating the WorkOrder in WIP.
For Complete Flow from SO to WIP , refer my existing blog http://eoracleapps.blogspot.com/2009/05/in-this-blog-i-will-explain-what-are.html