Re : So what I don't get is..
Re Scott's comment : "So does that mean that all car stereos and passengers are also going to be banned?"
Although I am by no means an expert on this topic, I once heard some 'experts' discussing this on Radio 4 and here's their answer (or hopefully the gist thereof....)
Research has shown that using a hands-free mobile phone while driving can reduce your driving ability to a level where it is worse than being over the drink-drive limit.
Under general boring driving conditions using a mobile phone may not pose too much of a problem but consider a situation where driving conditions change. For example, you approach a busy / complicated / unfamiliar junction, or traffic density increases suddenly. Basically, any situation where there is more information to process and decisions to be made.
When you are listening to the radio in the car, at any moment you have the choice to reduce how much attention your are paying to the radio and increase how much attention your are paying to driving. You will do this without really noticing.
When you are involved in a conversation with other passengers, they are also aware of current traffic conditions. They may choose to defer asking you a difficult question for a few minutes. They may pause an ongoing discussion. Most importantly, they will understand if you take a long pause mid-sentence because you have had to increase how much attention you are paying to driving, to the detriment of the conversation.
When you are involved in a conversation with someone on your hands-free mobile, they are not aware of current traffic conditions. They will not choose to defer asking you a difficult question for a few minutes. They will not pause an ongoing discussion. Most importantly, they will not understand if you take a long pause mid-sentence because you have had to increase how much attention you are paying to driving. You will feel awkward about pausing, and try to continue the conversation, to the detriment of your driving. It is in this scenario that tests have shown that your driving ability can reduce to a level where it is worse than being over the drink-drive limit.