Voice over Internet Protocol (VoIP) refers to technologies that provide voice communications services and data communications services (e.g., multimedia sessions) over Internet Protocol (IP) networks, such as the Internet and/or private packet networks. Other terms commonly associated with and used interchangeably with the term “VoIP” include “IP telephony,” “Internet telephony,” “broadband telephony,” and “broadband communications service.” An end-customer of an IP telephony provider may obtain a dedicated VoIP or IP telephony-compatible phone, which may be a stationary device (e.g., a hard-wired desk-top computer or telephone) or a mobile device. In another embodiment, an IP telephony customer may have a VoIP or IP telephony application installed onto a standard mobile communication device. For example, an installed IP telephony application may include a SIP (Session Initiation Protocol) client that enables IP telephony calls to be sent and received at a cellular mobile communication device. Typically, the installed IP telephony application indicates the telephone number that the IP telephony provider has assigned to its customer, and calls are originated and received by the customer's mobile device with reference to the assigned telephone number.
IP telephony technology, though, is not able to easily support various telephony features and capabilities that are provided by the Public Switched Telephone Network (PSTN). For example, to support emergency services calls to police, fire, ambulance, etc. (such as by dialing 9-1-1 in the United States), the direct relationship between a telephone number assigned to a land line telephone and the physical geographical location of the land line telephone is exploited in order to automatically provide the physical location of the caller to emergency responders. In IP telephony, though, no such direct relationship is guaranteed to be readily available, as assigned telephone numbers are typically mapped to IP addresses, and the respective physical locations of IP addresses may or may not be automatically tracked by Internet telephony service providers. Further, in some situations, unlike telephony numbers that are assigned to landline telephones, an IP address and/or assigned IP telephone number may not able to uniquely identify the physical location of a particular device. For example, when a IP telephony connection is a link to a virtual private network of an enterprise, the IP address used in end-user communications may identify the enterprise and not a particular end-user's device, and/or an assigned IP telephone number may be associated with an IP telephony application which may be executing on any one of a number of end-user devices.