ご返信が遅くなってしまいすみません。
ご安心ください。
「3GB以上通信した場合に制限がかかる」という事ではなく、
「3日間で3GB以上通信すると制限がかかる。」という事です。
(短い期間でいきなり大きな通信をすると、制限がかかってしまうようです)
万が一、速度制限がかかった後もWiFiはご利用可能です。
速度制限の期間中でも、目安としてYouTube動画の標準画質が見られるレベルで通信いただけます。
とても大きいファイルをダウンロードしたり、高画質の動画を見ないかぎりは、問題ありません。
Please rest assured that this does not mean "restricted after exceeding 3GB,"
it means "restricted after exceeding 3GB in the space of three days."
(The limit takes effect if your usage suddenly skyrockets within a short period of time.)
If you should exceed the limit, you can still use WiFi.
Even when the limit is in effect, you can still view YouTube videos at standard quality.
You can download very large files; as long as you are not viewing high-resolution videos, there is no problem.
Please feel at ease.
It does not mean that, "the limit is applied when you receive and transfer the data more than 3GB", but it means "the limit is applied when you receive and transfer the data more than 3GB in 1.consecutive three days".
(If you make huge amount of data sending and receiving in a short time, the limitation seems to be applied.)
Even if such limitation is applied by any possibility, WiFi is still available.
Even under the limited speed of connection, your connection speed enables you to watch YouTube movies in standard picture quality mode, for your reference.
It is not a big issue unless you download huge file, or, you watch high imaging quality moving pictures.
Please do not worry.
It doesn't mean that "limit applies in case of transmission over 3GB", instead, it means "limit applies if more than 3GB is transmitted in 3 days". (It seems like limit applies when large data is transmitted suddenly in short period.)
Just in case, after speed limit applies you can use Wi-Fi.
Even during limited speed, you can receive data enough to watch YouTube standard quality videos.
Unless you download huge file or watch high quality movie, there should be no problem.
"1.consecutive" は "consecutive" のタイプミスでした。失礼しました。