As far as just using your EIN to get a Business card that's not going to happen as it takes years to build "business credit". All new credit you're going to have to use the EIN to build the corps credit then also use your SSN. I don't know what the issue is with them dropping your limit on that personal one to 500$. I have 1 personal at 40k, 1 for one corp for 35k and 1 for my other corp for 50k. Both corps started in 08. So I think a lot has to do with your income and credit score. I've heard of them asking people to send their tax returns and stuff. But this hasn't happened to me yet. Wouldn't be a big deal just a pita.