Firstly you need to consider if you will use your home telephone number, set up a new line just for business use, perhaps use Skype (providing you have excellent broadband) or register a non geographic or 0844 number that will divert to your home number during office hours.
There are benefits to all options so consider each one carefully before making your choice. Don’t use more than one or they WILL all ring together!
Just a note about using a mobile telephone number, don’t use one for your main business number as it will destroy your credibility. It screams ‘one-man-band’. If you want to use a mobile, divert your landline to it using BT Call Divert.