As an iPhone user who travels often and uses a different SIM card in each country, I am experiencing effects of the same iOS defect. When I travel, the following occurs:
1. With iOS 5, I could simply switch SIM cards and iMessage would be immediately deactivated on Apple's servers for the previous SIM card's mobile number. Since iOS 6, I have to turn off iMessage and FaceTime before removing the previous SIM card. As an additional measure advised by Apple but which doesn't make much difference, I also sign out of my Apple ID for both iMessage and FaceTime before turning off both services.
2. When I arrive in the next country, I insert a SIM card local to that country.
3. My iPhone sends a chargeable international SMS text message to +44 7786 205094 and/or +44 7537 4102X1 (X can be any digit). These numbers are Apple's iMessage and FaceTime activation servers hosted by Vodafone UK for users in most countries. In iOS 5 and 6, the chargeable international SMS text message was sent only when iMessage and FaceTime were turned on, but it is sent immediately in iOS 7, giving the user no choice as to whether a charge will be incurred. Intermittently a warning pops up that the carrier might charge for iMessage and FaceTime activation, but this is too intermittent to be reliable.
4. I turn on iMessage and FaceTime and wait for both services to activate.
5. Very often the services fail to activate on the first attempt because of frequent intermittent problems affecting Apple's regional iMessage and FaceTime activation servers outside the United States. When this failure occurs, a workaround is to change one's wifi connection's DNS server temporarily to Google's US-based DNS server, 220.127.116.11, following which iMessage and FaceTime activate successfully via Apple's more reliable servers in the United States. More chargeable international SMS text messages are sent, incurring further financial loss.
6. When someone sends a text to the mobile number I was using in the previous country, their iPhone causes it to be sent inappropriately as iMessage rather than as SMS. Consequently these messages are undelivered and lost forever, but iOS even falsely indicates to the sender that the undelivered message was in fact delivered, even though I have no other iOS devices to which the message might have been delivered. I have experienced the same false delivery reports when I sent messages to other iPhone users who have switched SIM cards. This gives the false impression of rudeness by the recipient because the sender is misled that the recipient has received the message but has not responded.
7. While outside the UK, I want to reinsert my UK SIM card into my iPhone once per day and retrieve any SMS messages sent to my UK number, but this process is frustrated for two reasons: the issues above in step 3 whereby a SIM insertion charge is incurred, and the issues above in step 6 whereby other iPhones will have erroneously sent me messages as iMessage rather than as SMS.
I have reported these issues to Apple many times but they seem indifferent.