Does the iPhone 4 NEED a SIM card to be activated?

I bought my parents both iPhone 4 phones on eBay. They seem to be working just fine, it's just that it makes me connect to Wi-Fi and then one says "Activation Error" and on the other iPhone it says "SIM Required". Shouldn't both say the same thing?

Both iPhones need sim cards to be activated. It doesn't matter what each of them are saying, they both need sim cards in them.

Yes you need a valid SIM card to activate the phone then after activation you can safely remove the sim and use the phone