Yes
According to the National Allocation Plan of the Republic of Serbia, frequency band 876-880 MHz paired with 921-925 MHz is allocated to the GSM-R. However, GSM-R system is not implemented in Serbia yet
Yes
For further details (call signs, equivalent licences, other specific requirements) consult Annex 2 of T/R 61-01
Yes
For further details (national licences corresponding to HAREC etc) consult Annex 2 of T/R 61-02