Abstract: Transmission of voice over internet protocol is achieved in a Universal Mobile Telecommunications System (UMTS) by using a hybrid mode of attach whereby the speech bearer path from a mobile phone (1) is transported to the network controller (4) in circuit-switched mode and from thereonwards in packet mode. The control signalling from the mobile phone (1) is sent over the internet protocol to the core network (9). The invention has the advantage of providing the optimised speech path by using the most appropriate parts of existing circuit-switched and packet-switched domains, thus, enabling voice calls, facsimile transmissions and computer-generated data to be transported over a single data network.