There is no more requirement to carry a radio than there is to have life jackets on board ...
It is up to the individual to equip the boat to his/her own standards.
Although you dont NEED a VHF, they can be very useful.
Radar - great bit of kit - wish I could afford one! Handy if you know how to use it properly - doesn't replace the VHF though
EPRIB - great again ... for emergency use only, will allow the emergency services to home in on you ... but they can't talk to you through it.
The 3km radio - unless this operates on the licence free channels then it does require a licence - to have and to operate - if it works on the free channels then is it really of any use?
Mobile phone - ok if you have a signal, but is one2one rather than one2many - ie only the person you phone can hear you.... and the helecopter/lifeboat won't find it easy to contact you by it, cannot home in on it (ok so you have an EPRIB) and is certainly not the preferred choice of contact method.
As I said in the other thread - having a VHF (not nessersarily DSC) also adds an element of safety to other craft around you - if you are monitoring Chl16 and could relay/render assistance when they are in trouble....