I have two vodafone sims in two different phones, one for business, and one for personal. I swapped the sim out in the weekend in my iphone, and found that when this happens, the iphone sends a 31 cent international txt for authenticating imessage,. So it apparently sends multiple texts for authenticating both imessgae and facetime . When I switched the sims back, the same thing happened. Vodafone are aware of this, but are happy to continue to charge this. Infact it looks like their international txt rate has increased, as I am sure it used to be 20 cents, now it is 31 cents. From what I have read on the vodafone and apple forums, overseas telcos don't charge for this, as they have an agreement with Apple. But that doesn't appear to be the case in NZ. There is no warning of these charges anywhere. Why Apple doesn't have a local number in NZ that it txts, I don't know

This is vodafones explanation for the problem

The $0.31 international TXT was for the silent SMS sent by your iPhone device to register your details to the server located in UK. It occurs when you register to FaceTime or iMessage or if you make changes with your phone set-up. Subsequent resetting of FaceTime settings, or completing a SIM swap, may cause FaceTime to send another registration SMS.
 
Vodafone are unable to prevent the SMS from being sent due to the default registration number (00447786205094) routing the SMS request to the UK. Further charges will be incurred if multiple registration requests are sent from the iPhone.


Should this be disclosed by the  retailer or in the phone documentation, to people buying iphones, as to me this seems to be a hidden fee, and Apple didn't ask my permission to send an international txt message. What can be done to stop being charged. Do other NZ telcos charge this as well?