You cannot change the default view to "Inbox" or any other folder. The default view will always be all messages. You can tweak this by hiding sent messages and filed messages, but as long as the messages are un-read they will appear anyway.
A solution for you could be: Create a Saved Search with "Inbox" as search criteria and assign it a key. When you are in your messages, you can easily get to your Inbox by hitting ALT + key. See details on:
Saved Searches - BlackBerry Tips