Setting carrier and country restrictions
You can set restrictions for your app on the carriers that offer it, and in the countries where it's made available. Without any distribution restrictions, your application will be available on all carriers and in all countries BlackBerry World is available.
Consider choosing the widest distribution and the most wireless service providers (carriers) you can. For example, if you have a newspaper application that highlights a geographic region, but you have rights to distribute it worldwide, then you could increase visibility and generate more downloads by clicking Available on all carriers, and Available in all countries.
Restrictions are typically related to the distribution rights you hold for your app's content.