G-Benz is correct about carriers charging a fee for WNP. There are significant network costs to this capability that the government has mandated and supplied NO money for. If you port your number from your existing carrier to a new carrier, all of your calls will hit the incumbent carrier's switch and then be directed to your new carriers switch. This means that the incumbent carrier's switching resources will be tied up to redirect a call that does not generate any revenue for them.

There are several other unfunded government mandates on wireless carriers as well CALEA being one of them along with E911. All the costs associated with these programs must be borne by the carrier unless they decide to share the burden with the consumer (who derives all the benefits of these programs). Not to complain about them, but if/when you do see a charge for something like this, understand what is going on behind it.