iPhone 5 on contract with VDF. When in UK I can receive and send text messages (inc iMessages) without problem. However when I go abroad I can receive texts OK but I cannot send texts. The Message Send Failure comes up and Not Delivered. iMessages works OK. The VDF shops seem to be helpless in providing a resolution. The thing is that you can only test if it works when you go abroad - only to find it does not work. My wife has O2 which works perfectly. Any Expert at VDF who can help solve this?