In majority of the project proposal I been reading through the users always need internet connection and in some cases using Apps in car. I am not sure how its possible, defiantly not in my countries of resident (UK and many more in Europe). The idea shall be expanded into Nav System, where the driver can have an easy view on and not get court of fine.
Secondly, how big is the market of those who will use 3G or 4G on their phone and how much are they willing to spend per month on recieving data on their phone? Facebook/Twitter do not consume much data, but some of those ideas I seen they can use maybe already over 10MB of data. I am on Pay as You Go (credits) and only given of an allowance of 20MB per month, this is enough to Facebook, read Newspapers and read Emails.
It would be interesting to know how much data allowance and even storage space on the phone, a user will give up to improve its city environment by using such technology.