What SIM card do I need for an iphone 4?

I'm a Verizon customer and want to upgrade my current cell phone to the iphone 4. I have already purchased the iphone. In order to set it up, it says I need a SIM card. What is the exact type of card I need for this phone to work with Verizon? What is the exact title and what do I need to look for when purchasing it? I'm probably going to look to buy on ebay first. Also, will this phone work with Verizon?

Added (1). Thanks. Just sold it and made an extra $50 over what I paid for it. Ordered one through verizon.

You need nano sim card means the golden part of chip

Verizon is a CDMA network which does not use SIM cards. Sounds like you bought an AT&T model which does use them since they are a GSM network. You would have to sell that one & get a Verizon iPhone 4 & have them activate it.

For the sake of answering the question though the iPhone 4 uses microSIMs.

You bought an att iphone, can't use it on Verizon.