distinct from a cellular phone in two major areas: WiFi phones run over 802.11a, b, g, or n WiFi frequencies instead of the traditional GSM or CDMA bands. This physical difference limits the long-range capabilities and deterministic quality of WiFi phones. WiFi phones are homed or controlled by the enterprise IP-PBX and not an SP. This enables for much greater flexibility in terms of endpoint features. Other than these two unique capabilities of WiFi phones, their advancement is moving in the same general direction of mobile phones. That is, they are becoming lighter, rugged, and longer lasting as technology advances. WiFi phones have better screens for display- ing information about a call and are improving their integration with Bluetooth as a method to offload the audio playback to another device, gaining a great deal of nontradi- tional phone features. These nontraditional phone features generally relate to the use of the phone as a mobile application platform. As an application platform, one of the unique capabilities of a phone is that it is locations-aware. This leads to advanced applications, such as the capability to display ads for stores that you are physically close to. These trends require that SIP trunk providers and consumers take into account that some of their endpoints might be WiFi phones because they have different capabilities that must be considered, such as the following: Being mobile, they have a tendency to change audio characteristics within a call. This would mean that to take advantage of this, the SIP trunk might need the capability to read and determine that the signal strength is weakening and switch over to a lower bandwidth codec. This is done in the cellular world but has not been adopted in the SIP trunking area. However, this adaptation could occur at either the premise IP-PBX or the SP network. 18 SIP Trunking The IP endpoint is no longer likely to be stationary; as such, the capability to receive the location along with the call setup should be something that is offered. This