That would depend on the source of the charge. On your bill it will show as wap, but sometimes there's also 3rd party subscription services listed. You would have to cancel the subscription services to not be charged through them. Also, deending on your device, whether or not you have a messaging plan will also count, such is the case with sending MMS which exceeds a certain size. All MMS uses data to send, so you may incur data charges in doing so.