Unlock codes for Verizon phones are granted on request by calling 1-800-711-8300. As of April 2015, Verizon does not have an online unlock request form.
According to Verizon's device unlocking policy, most phones or tablets that are activated with its postpay service are not locked. The same applies for its prepaid devices. The non-iPhone Global Ready 3G phones are locked, but other than these, Verizon doesn't lock its 3G devices.
The code to program the locked 3G devices for use with other carriers is usually ?000000? or ?123456.? However, Verizon's 3G prepaid phone-in-the-box phones are restricted for use with Verizon's prepaid service for six months after activation, and they are locked to the Verizon Wireless network for 12 months after activation. The restriction to its prepaid service is automatically removed after six months.