These text messages are associated with the use of the Apple applications Facetime or iMessage. Your iPhone sends these to activate a text message to the Apple servers (that is not in the messages sent). These are located in the United Kingdom. This is where the Facetime server is located.
When you use these apps, you receive a pop-up on your screen that indicates that a text message might be sent to activate the service. When you accept the general terms and conditions for these applications, you agree to pay for these text messages.
To prevent this from happening in the future, we recommend that you carefully read all of the information when you download or use and application.