Porting your wireless phone number to another carrier will require you to provide a current account number and PIN for that number. These two seemingly simple items delay more ports than any other error or issue we see.
Most carriers do a good job of providing you with an easy way to get your account information (on your bill, online account, etc), but there are a select bunch that make it a little more difficult than others. Here's a resource that walks you through how to find that information:
Otherwise, it may be best to contact the carrier to get your account number and PIN if it's not readily available on your bill or in your online account.