$400 voucher is being advertised but Westfield Chatswood is throwing in an extra $100 and making it $500. Today and tomorrow only I was told.
Mod: Note that the OP is associated with JB Hi-Fi and posted the deal for Westfield Chatswood only, however comments indicate that it's available Australia wide. Check with your local store. Deal updated.
@neilpatrickharris: Yes. Signed up for the plan during my lunch break and hopped on Telstra 24x7 chat shortly after my number was ported over (about 30 minutes)