If you find that your iPhone has started showing phone numbers in the wrong international format, or has decided your phone is a Swedish phone with a +46 extension there's a very quick fix.
Open Settings on your iPhone, head to Phone and then "My Number". Change this from +44 7xxx xxxxxx to +44 (0) 7xxx xxxxxx. You may also need to head into Settings -> General -> Language & Region and then switch the Region from UK to US and back to UK. This will revert all your contacts to their normal formatting and get Caller ID working again.
It's an issue we're aware of and are looking to get fixed as quickly as possible.
On Android, head to: Dialer > Settings > Assisted Dialing >Default country/region code > Set automatically detected to off > Select England. This will set your region back to the UK and you should find your phone is working as normal again.