[amirmc]

In the UK, 'mobile hailing' would be equivalent to pre-booking. In many parts of the UK pre-booked cabs are referred to as Private Hire vehicles. The only cabs you can hail on the street are Hackney Carriages. I believe unlicensed minicabs are illegal in the UK but London still seems to have problems with them.

For both Private Hire and Hackney Carriages, the cars/drivers are licensed and must meet regulatory requirements regarding vehicles and insurance policies. I believe the requirements for Hackney Carriages are more stringent.

Those licences exist to protect the public.

For both types of licensed drivers, UberCab would be a great extension. However, I can only imagine it working if the taxi firms themselves were willing to implement it.