Setting the callback URL to oob means providing a signed oauth_callback parameter to the oauth/request_token endpoint with the value “oob” – instructing Twitter that the auth sequence will be of the out-of-band variety, resulting in the user being displayed a PIN code that they must enter into your application so that you may then exchange a request token for an access token.
Likely not the sequence you want on an Android device.
Find out how to register a URI scheme for your application on Android. Use this URI scheme and a specific “path” in your application as the oauth_callback value on the oauth/request_token step. If you’re using this approach, you’ll need to provide a place holder HTTP-based URL in the callback field of your dev.twitter.com application record.