A number of years ago when I worked for a Worcestershire based two way radio company, mobile phones were starting to seem a viable alternative to two way radio for large organisations such as councils.
Indeed some council departments and private companies replaced their free to call, two way radios with mobile phones, believing that the call packages offered by the mobile phone companies would work out cheaper than the cost of maintaining a fleet of two way radios.
What happened was that they had no control over call cost expenses, and it was expensive, slow and almost impossible to send a ‘group message’ from the base controller to all personnel quickly.
An example was in an emergency situation when you did not want you vehicles and employees to be in a certain location. With mobile phones it was slow and inconvenient to have to call up each employee, whereas with two way radio, all users could be contacted simultaneously which aids safety in an emergency, and has no call costs involved.