There are several legal options available to you. Firstly, do not use your mobile phone at all if you are driving! That is the advise from road safety organisations, yet that is not allot of use for drivers who are dependent on mobiles for their day to day business. A Second choice may be a bluetooth headset, but be sure to have a fixed holder or cradle for your mobile  to sit in, as you are not allowed to hold it to make calls whilst driving, even if you are using a bluetooth ear peace. Thirdly -and this is the preferred solution to thousands of professional drivers across the UK is a fully fitted bluetooth handsfree car kit, but again, as above, make sure you have a fixed holder for your mobile to avoid falling foul of current legislation!