Because we want your phone to work on your carrier of choice
When we sell you a phone for use on a certain carrier, we guarantee that the phone will be able to activate on the carrier you've selected. If you bought your iPhone for use on Net10 service, you can expect that you will have a working iPhone on Net10 when all is said and done.
We'll even call Customer Service for you and handle the activation / transfer if necessary. Let's see the other guys do that.