The present invention relates to a method of arranging inter-working for a communications system comprising a PMR (private mobile radio) system part and a PLMN (public land mobile network) system part. The system comprises a mobile intermediate device capable of communicating with the PMR system part and the PLMN system part and comprising a converter for performing protocol conversion between the PMR system part and the PLMN system part, the method comprising: detecting in the intermediate device a need for inter-system transfer from a source system part to a target system part, performing by the converter conversion for an information unit from a source system to a format appropriate in the target system part; and transmitting the converted information unit to the target system part.