Be careful with that, as many years ago, due to not using the landline because of having the mobile, BT actually charged me for Caller Display or something similar, which was normally free, as I had not made two chargeable calls in the previous three months WTF!
Let's hope they put a simple 'Please re-dial putting 01273 first' message on all failed calls, for the elderly and infirm of mind, so the transition isn't too taxing ???