WHY WHY WHY did I only check this forum now!
I just tried to get an account and got:
Aventure Mail Error
We are currently not accepting new registrations. Accounts can be purchased in our store (
http://www.aventuremail.co.uk/store) in the mean time.
So only 'paid-for' accounts for the moment (3GB/4GB/5GB for $21.95/$41.95/$65.95 respectively)