Is there a way of me knowing if it's a customer calling when pointed to my landline or mobile?

Normally, the caller’s number will show on your phone screen and this may be enough for you to determine whether this is a customer or a friend.

If you would like to know what number the caller has dialled before you answer, you will need Dialled Number Identifier (DNI). This is available at a cost of £9.95 set up and £2.50 per month. It can be set up within the number management area of your online account.