Not only can you sign up with a different card (credit or debit), but it can be useful to be in more than one airline's iDine program for two reasons:

1. iDine's 1/month restaurants are only 1/month PER AIRLINE. So you can dine in July once at a 1/month restaurant using the card linked to your CO iDine account, and then dine again in July once at the same restaurant, and if you se the card linked to your AA iDIne account you'll get miles whereas if you use the card linked to your CO iDine account again you'll get nothing.

2. iDine doesn't run bonuses the same month at every airline, and in fact they often have months where they'll have bonuses at AA but not at CO or vice versa (or at least much better bonuses, for whatever way you use iDine, at one than the other).

Did CO have the ability to earn 25 miles per dollar spent for EVERY DINE (no minimum limit) from late may through the end of June (if you were top tier at AA iDine already by then)?

Does CO right now have the ability to earn 1000 bonus miles for just 4 dines (no miminum limit)? (That's the bonus at AAdvantage Dining now through the end of August. Not a great bonus for those of us who like AA as our PRIMARY iDIne airline, since if you go beyond 4 dines there's no further bonus, but a great bonus if you're using AA as a SECONDARY iDIne airline.)