A system comprising: a device presence proxy in a network; a first plurality of mobile devices (12A,12B) including a first client application loaded on said devices, each instance of said first client application being arranged to communicate with an application server for said first client application; a second plurality of mobile devices including a second client application loaded on said devices, each instance of said second client application being arranged to communicate with a device presence application programming interface, API in the device presence proxy via a device presence API on the mobile device; and at least one application server, the or each application server being operable to communicate with instances of said first client application on said first plurality of mobile devices, the or each application server being arranged to communicate with the device presence API in the device presence proxy via a device presence API on the or each application server; the device presence proxy comprising said device presence API providing information to subscriber devices including each of said at least one application server and said second plurality of mobile devices and being arranged to: receive, via the device presence API, a subscription request, the subscription request requesting a presence data for at least one mobile device (12, 12B); register a subscription for a subscriber device according to the subscription request; obtain network data from one or more network infrastructure nodes associated with providing service to the at least one mobile device (12, 12B); determine that at least a portion of the network data is associated with the subscription; and in dependence upon said determination, provide the at least a portion of the network data to the subscriber device as an indication of presence information for the at least one mobile device via the device presence API. a device presence proxy in a network; a first plurality of mobile devices (12A,12B) including a first client application loaded on said devices, each instance of said first client application being arranged to communicate with an application server for said first client application; a second plurality of mobile devices including a second client application loaded on said devices, each instance of said second client application being arranged to communicate with a device presence application programming interface, API in the device presence proxy via a device presence API on the mobile device; and at least one application server, the or each application server being operable to communicate with instances of said first client application on said first plurality of mobile devices, the or each application server being arranged to communicate with the device presence API in the device presence proxy via a device presence API on the or each application server; receive, via the device presence API, a subscription request, the subscription request requesting a presence data for at least one mobile device (12, 12B); register a subscription for a subscriber device according to the subscription request; obtain network data from one or more network infrastructure nodes associated with providing service to the at least one mobile device (12, 12B); determine that at least a portion of the network data is associated with the subscription; and in dependence upon said determination, provide the at least a portion of the network data to the subscriber device as an indication of presence information for the at least one mobile device via the device presence API.