For iStore, each iStore Customer responsibility (ie IBE_CUSTOMER, IBE_CUSTOMER_UK) is tied to one operating unit and this is where the order is placed. There is no option for a user to choose the operating unit. The setting in the profile option 'MO:Operating Unit' for each customer responsibility is used to determine the operating unit.
Please see these documents which are relevant for both 11i and Release 12 ** -
Understanding Oracle iStore in a Multi-Operating Unit Environment (Doc ID 139347.1)
11.5.10: How To Setup Oracle iStore for a New Operating Unit and Item Master in a Multi Org Environment(Doc ID 265772.1)
** For Release 12 there is also the 'MO:Security Profile' profile option, see examples in the iStore documenation -
And see section "Step 3 - Set up Oracle iStore Customer Application Responsibilities"