A method of facilitating establishment of a telecommunication transaction using a mobile device, the method comprising: launching an application for remotely managing private branch exchange, PBX, functionality on the mobile device, wherein the launching is in response to a request from a user of the mobile device, and wherein the application comprises a user interface that enables the user to initiate telecommunications transactions; receiving, by a server, a call control request for a telecommunications transaction from the mobile device, wherein the request uses a data network protocol and is received via a call control channel separate from bulk voice transport, wherein the bulk voice transport comprises at least one voice channel to transport voice data; retrieving (40, 70, 72), by the server, a callback identifier for the user, which is to be used in the requested telecommunications transaction, wherein the callback identifier represents a callback telephony endpoint, wherein the application enables the user to select the callback telephony endpoint for the requested telecommunications transaction, where the callback telephony endpoint is selectable from among the mobile device and one or more other telecommunications devices; and executing (74, 80, 84, 90), by at least the server, the telecommunications transaction, wherein the executing occurs subsequent to the call control request being received, and wherein executing the transaction comprises: establishing a communications session that includes the callback telephony endpoint represented by the callback identifier and at least one target telephony endpoint indicated by the user, wherein a first portion of the communications session that includes the callback telephony endpoint is established at least in part by making an outbound call from a PBX associated with the user, via the bulk voice transport, to the callback telephony endpoint, and a second portion of the communications session that includes the target telephony endpoint is established at least in part by making an outbound call from the PBX, via the bulk voice transport, to the target telephony endpoint. launching an application for remotely managing private branch exchange, PBX, functionality on the mobile device, wherein the launching is in response to a request from a user of the mobile device, and wherein the application comprises a user interface that enables the user to initiate telecommunications transactions; receiving, by a server, a call control request for a telecommunications transaction from the mobile device, wherein the request uses a data network protocol and is received via a call control channel separate from bulk voice transport, wherein the bulk voice transport comprises at least one voice channel to transport voice data; retrieving (40, 70, 72), by the server, a callback identifier for the user, which is to be used in the requested telecommunications transaction, wherein the callback identifier represents a callback telephony endpoint, wherein the application enables the user to select the callback telephony endpoint for the requested telecommunications transaction, where the callback telephony endpoint is selectable from among the mobile device and one or more other telecommunications devices; and executing (74, 80, 84, 90), by at least the server, the telecommunications transaction, wherein the executing occurs subsequent to the call control request being received, and wherein executing the transaction comprises: establishing a communications session that includes the callback telephony endpoint represented by the callback identifier and at least one target telephony endpoint indicated by the user, wherein a first portion of the communications session that includes the callback telephony endpoint is established at least in part by making an outbound call from a PBX associated with the user, via the bulk voice transport, to the callback telephony endpoint, and a second portion of the communications session that includes the target telephony endpoint is established at least in part by making an outbound call from the PBX, via the bulk voice transport, to the target telephony endpoint. establishing a communications session that includes the callback telephony endpoint represented by the callback identifier and at least one target telephony endpoint indicated by the user, wherein a first portion of the communications session that includes the callback telephony endpoint is established at least in part by making an outbound call from a PBX associated with the user, via the bulk voice transport, to the callback telephony endpoint, and a second portion of the communications session that includes the target telephony endpoint is established at least in part by making an outbound call from the PBX, via the bulk voice transport, to the target telephony endpoint.