I also am on the old unlimited package, and I wondered the same, however i found this on the wannado broadband faq page. Quote:
"Does Wanadoo still have a £27.99 a month broadband product with no usage limit?
This product is no longer available to new customers - if you're already on this product you can stay on it or switch to one of our new broadband services."
So I think that answers your question?
Here is the link to the page I found. click here