Using 0845 numbers on your website and only on your website allows you to track how many people are calling you as a result of having seen your website.

The calls can only come from your website as that is the only place you have advertised it.

The 0845 numbers allow you to receive calls to any location in the country as they are non geographic numbers that are able to give you a wide range of statistics on the calls you receive including the number called from (so long as they have not chosen to hide it), duration of the call, was the call answered, the time and date of the call.

Using this information you can target your on-line marketing to get the best responses, you can ascertain where in the country people are calling from, see if you need more people answering the phones, check when peak times are and much more.

I can highly recommend Windsor telecom if you are interested in using 0845 numbers as they have the best reporting software I have seen.