Is A Sim Card Required to Use An iPhone 5C?(For iPhone 5C Users)?

My Mom is buying me a blue iPhone 5C, and I was wondering if a Sim Card is required to use the Phone. I mean, the iPhone 5C doesn't come with a Some Card, so maybe it's optional to use, or maybe they don't put it in there even though you need it and they make you go out and buy it, but I honestly don't know. So please, people out there who have an iPhone 5C, is a Sim Card Required to use an iPhone 5C?

It depends on the carrier you are on.

Ones like Verizon/Sprint - no, because they are CDMA
Ones like AT&T/T-Mobile, yes, because they are GSM