Can i factory un lock my iphone 4?

My iphone is verizon and i need to switch it to at&t. Is there a way i could do it? And possibly a free way i would really appreciate it!

Yes, you can unlock it, but it still would not work, because Verizon is a CDMA network, and ATT is a GSM network, and GSM networks take a sim card, and CDMA does not. They are not compatible with each other.

1. You can't factory unlock your phone. Only the carrier.
2. The iPhone 4 is either CDMA (Verizon) or GSM (AT&T). Not both. Can't switch between the 2.