I don’t see a reference to it on their website, but his commenters confirm that it’s noted in their welcome email.
You want to open an Iberia Plus account:
- Because when an account has been open for 90 days and has had any activity you can transfer British Airways Avios over to Iberia Avios.
- Iberia doesn’t add significant fuel surcharges onto Iberia flight redemptions. So you save most of the cash cost you’d spend with British Airways points to book Iberia, by transferring your points to your Iberia account and booking the same flight.
- Iberia runs award discounts that can make transatlantic premium cabin flying quite cheap. (They often have quite good award availability.)
You don’t have to credit a flight (such as US Airways or American) to get some activity in your account. You can get activity in an Iberia account quite easily by transferring in 1000 American Express Membership Rewards points. Or credit a car rental, e.g. Avis is an Iberia earning partner.