If you have HG/SS then you will have access to a couple of events in the coming weeks.

Mew will be available to download off Wi-Fi through Mystery Gift from November 11th to November 23rd. This Mew will be at level 5, know the move Pound and have the Premier Ribbon.
This Even will then be Released for D/P/Pt gamers from the 29th January to the 11th February

The second Event will be the Enigma Crystal Event.
This too will be downloaded from Wi-Fi Mystery Gift from November 11th to January 29th.
After getting the Enigma Crystal, take it to the Pewter Museum to the guy who revives fossils then it will be exchanged for the Soul Dew. Steven Stone will then appear and tell you it's an incarnation of Latias/Latios's Soul. Once you leave Latias (In Soul Silver) and Latios (In Heart Gold) will attack you. They will be at level 35.
Click here to see the Serebii Page.