Yes when you pre-order you will be assigned a new Verizon phone number. Once you try out Verizon service in all the places you expect to use your new iPhone then you call the Verizon automated porting number: 866-465-5415 and follow the automated prompts to enter the following information. You can also call Customer Support and they can assist you.
Note: You will need to know your AT&T account information so take a few minutes to gather the details:
1.Your AT&T account number
2.Your AT&T account secret PIN (if you have one assigned)
3.The last 4 digits of the account holders SSN
4.Your new (temporary) Verizon phone number
5.Your old AT&T number you'd like to port over