You might get an unlimited rental if you book through an intermediary.
I've booked in the NT through billiger-mietwagen.de and had a voucher with unlimited miles (Europcar) - although billiger-mietwagen.de are usually fine, this time the voucher was not honoured by Europcar. They told me that the "travel agent" had cancelled the booking, which billiger-mietwagen.de denies. Being stuck at the airport of ASP I had to make a new contract and now I'm in the process of getting my money back from billiger-mietwagen.de...