The default keys like T, Y, U, and B are auto-bound by the MTA client for chat commands You can change them using a clientside script first unbind the key then bind it to your radio command For example :
-- Unbind the default team chat key
unbindKey("t", "down")
-- Bind T key to run your radio command
bindKey("t", "down", function()
executeCommandHandler("radio")
end)
You can do the same for Y, U, B, etc. This will override the default chat binds on your server while players are connected