We have put together a short survey to capture your feedback in terms of what BT can do when you experience home Wi-Fi issues. We would appreciate it if you could take a couple of minutes to complete a short survey. Read more from here, Fix my home Wi-Fi
Did you enable roaming and Intenational calls before you left the UK? Its done via MyBT.
Thanks guys your lifesavers, all working now. I must of blocked international calls and forgot. I turned it back on under my by BT.
I had to go into iPhone settings and turn off automatic carrier selection, once I selected T-Mobile it started working.