TwitterCore twitterCore = TwitterCore.getInstance();
twitterCore.logIn(activity, new Callback<TwitterSession>() {
    @Override
    public void success(Result<TwitterSession> result) {
        // ログイン処理に成功
    }

    @Override
    public void failure(TwitterException e) {
        // ログイン処理に失敗
    }
})

TwitterSession twitterSession = TwitterCore.getInstance().getSessionManager().getActiveSession();
StatusesService statusesService = new TwitterApiClient(twitterSession).getStatusesService();
statusesService.update("Tweet Message.", null, false, null, null, null, false, false, new Callback<Tweet>() {
    @Override
    public void success(Result<Tweet> result) {
        // 投稿処理成功
    }

    @Override
    public void failure(TwitterException e) {
        // 投稿処理失敗
    }
});

public interface SKNStatusesService {
...
@FormUrlEncoded
@POST("/1.1/statuses/update.json")
void update(
@Field("status") String status,
@Field("in_reply_to_status_id") Long inReplyToStatusId,
@Field("possibly_sensitive") Boolean possiblySensitive,
@Field("lat") Double lat,
@Field("long") Double longDouble,
@Field("place_id") String placeId,
@Field("display_cooridnates") Boolean displayCooridnates,
@Field("trim_user") Boolean trimUser,
@Field("media_ids") String mediaIds,
Callback<Tweet> cb);

public class SKNTwitterApiClient extends TwitterApiClient {
...
public SKNStatusesService getfalStatusesService() {
    return (SKNLStatusesService)this.getService(SKNStatusesService.class);
}

TwitterSession twitterSession = TwitterCore.getInstance().getSessionManager().getActiveSession();
SKNStatusesService statusesService = new SKNTwitterApiClient(twitterSession).getfalStatusesService();
statusesService.update("Tweet Message.", null, false, null, null, null, false, false, "media_id_string1,media_id_string2,media_id_string3,media_id_string4", new Callback<Tweet>() {
    @Override
    public void success(Result<Tweet> result) {
        // 投稿処理成功
    }

    @Override
    public void failure(TwitterException e) {
        // 投稿処理失敗
    }
});

public interface SKNMediaService {
...
@Multipart
@POST("/1.1/media/upload.json")
void upload(@Part("media") TypedFile media, Callback<Media> cb);

public class Media {
    @SerializedName("media_id")
    public final long mediaId;
    @SerializedName("media_id_string")
    public final String mediaIdString;
    @SerializedName("size")
    public final long size;
    @SerializedName("image")
    public final Media.Image image;

    public Media(long mediaId, String mediaIdString, long size, Image image) {
        this.mediaId = mediaId;
        this.mediaIdString = mediaIdString;
        this.size = size;
        this.image = image;
    }

    public static class Image {
        @SerializedName("w")
        public final long width;
        @SerializedName("h")
        public final long height;
        @SerializedName("image_type")
        public final String imageType;

        public Image(long width, long height, String imageType) {
            this.width = width;
            this.height = height;
            this.imageType = imageType;
        }
    }
}

public class SKNTwitterUploadApiClient {
...
    final ConcurrentHashMap<Class, Object> services;
    final RestAdapter adapter;

    static final String TWITTER_API_HOST_NAME = "https://upload.twitter.com";

    SKNTwitterUploadApiClient(TwitterAuthConfig authConfig, Session session, TwitterApi twitterApi, SSLSocketFactory sslSocketFactory, ExecutorService executorService) {
        if(session == null) {
            throw new IllegalArgumentException("Session must not be null.");
        } else {
            this.services = new ConcurrentHashMap();
            Gson gson = (new GsonBuilder()).registerTypeAdapterFactory(new SafeListAdapter()).registerTypeAdapterFactory(new SafeMapAdapter()).create();
            this.adapter = (new RestAdapter.Builder()).setClient(new AuthenticatedClient(authConfig, session, sslSocketFactory)).setEndpoint(twitterApi.getBaseHostUrl()).setConverter(new GsonConverter(gson)).setExecutors(executorService, new MainThreadExecutor()).build();
        }
    }

    public SKNTwitterUploadApiClient(Session session) {
        this(TwitterCore.getInstance().getAuthConfig(), session, new TwitterApi(TWITTER_API_HOST_NAME), TwitterCore.getInstance().getSSLSocketFactory(), TwitterCore.getInstance().getFabric().getExecutorService());
    }

    public SKNMediaService getMediaService() {
        return (SKNMediaService)this.getService(SKNMediaService.class);
    }

    protected <T> T getService(Class<T> cls) {
        if(!this.services.contains(cls)) {
            this.services.putIfAbsent(cls, this.adapter.create(cls));
        }

        return (T) this.services.get(cls);
    }s

File mediaFile ...
TypedFile typedFile = new TypedFile("multipart/form-data", mediaFfile);
...

TwitterSession twitterSession = TwitterCore.getInstance().getSessionManager().getActiveSession();
SKNMediaService mediaService = new SKNTwitterUploadAPIClient(twitterSession).getMediaService();
mediaService.upload(typedFile, new Callback<Media>() {
    @Override
    public void success(Result<Media> result) {
        // メディア登録完了           
    }

    @Override
    public void failure(TwitterException e) {
        // メディア登録失敗
    }
});