Do I need a sim card to activate iphone 4s?

So I'm about to buy a used iphone 4s for cricket but the phone doesn't come with a sim card.
Is that a major problem? Do I even need it? If so where can I buy one for cricket wireless?

No, cricket is a CDMA network which means no SIM cards. Take it to a Cricket store and have them activate it.

SIM cards canot be reacticated so you need a new sim