not generally caught on. A more popular approach has been full-spectrum handsets that can communicate with any wireless network including mobile VoIP, DECT and satellite phone networks, but which have limited handoff capabilities between networks. The intent of IEEE 802.21 and IEEE 802.11u is that they be added to such phones running iPhone, QNX, Android or other smartphone operating systems, yielding a phone that is capable of communicating with literally any digital network and maintaining a continuous call at high reliability at a low access cost. Most VoIP vendors implement proprietary technologies that permit such handoff between equipment of their own manufacture, e.g. the Viera system from Panasonic. Typically providing mobility costs more, e.g., the Panasonic VoIP cordless phone system (KX-TGP) costs approximately three times more than its popular DECT PSTN equivalent (KX-TGA). Some companies, including Cisco, offer adapters for analog/DECT phones as alternatives to their expensive cordless. Industry history 2005 Early experiments proved that VoIP was practical and could be routed by Asterisk even on low-end routers like the Linksys WRT54G series. Suggesting a mesh network (e.g. WDS) composed of such cheap devices could similarly support roaming mobile VoIP phones. These experiments, and others for IP roaming such as Sputnik, were the beginning of the 5G protocol suite including IEEE 802.21 and IEEE 802.11u. At this time, some mobile operators attempted to restrict IP tethering and VoIP use on their networks, often by deliberately introducing high latency into data communications making it useless for voice traffic. 2006 In the summer of 2006, a SIP (Session Initiation Protocol) stack was introduced and a VoIP client in Nokia E-series dual-mode Wi-Fi handsets (Nokia E60, Nokia E61, Nokia E70). The SIP stack and client have since been introduced in many more E and N-series dual-mode Wi-Fi handsets, most notably the Nokia N95 which has been very popular in Europe. Various services use these handsets. 2008 In spring 2008 Nokia introduced a built in SIP VoIP client for the very first time to the mass market device (Nokia 6300i) running Series 40 operating system. Later that year (Nokia 6260 Slide was introduced introducing slightly updated SIP VoIP client. Nokia maintains a list of all phones that have an integrated VoIP client in Forum Nokia. Aircell's battle with some companies allowing VoIP calls on flights is another example of the growing conflict of interest between incumbent operators and new VoIP operators. 2009 By January