It is not always possible or appropriate for the best person to speak to new potential clients be available in the office 24 x 7 x 365. It is also possible you are unable to add a dedicated land line to your office space due to restrictions or high cost.
It is also rarely ideal to publish a mobile telephone number.
You can have a choice of memorable local area, 0800, 0845 or more telephone numbers and more online within only 48 hours, redirected to mobile or VOIP (Skype). You then publish this new number on your web site and your printed literature meaning you never miss a call but still show your clients you are serious. Also events such as moving premises or your landline failing does not effect you as you can route calls to a landline or mobile, effectively automatically taking this number with you.