Assuming that there is a number on the bill that you do not want someone to see, there is a setting in the My O2 app which displays calls using the name in your contacts, and not the number dialled.
So if you were to store this number in your contacts as "john smith" for example, then that is how the the call would appear in My O2. If you choose the name of someone that you normally call, then this would look quite normal.
Note - the above does not affect how calls are displayed on paper or PDF bills, nor on the online bills outside of the My O2 app, where the dialled number will be displayed.
Hope this helps!
