Few grammatical issues, recommend changing to: 

>  When paying for a product or service via [carrier billing](http://en.wikipedia.org/wiki/Mobile_payment#Direct_operator_billing), the carrier needs to confirm with the user before their account is charged. This is done by proving the user is in possession of the authorized SIM at the time of purchase.

I.e., it's not really dependent on the phone, as it could be any device that excepts a SIM card. 

The above can probably be improved a little more.