Mobile VoIP is an extension of mobility to a VoIP Voice over IP network.

There are several methodologies by which a mobile handset can be integrated into a VoIP network. One implementation turns the mobile device into a standard SIP client, which then uses a data network to send and receive SIP messaging, and to send and receive RTP for the voice path. This methodology of turning a mobile handset into a standard SIP client requires that the mobile handset support, at minimum, high speed IP communications. In this application, standard VoIP protocols (typically SIP) are used over any broadband IP-capable wireless network connection such as EVDO rev A (which is symmetrical high speed — both high speed up and down), HSDPA, WiFi or WiMAX.

Another implementation of mobile integration uses a softswitch like gateway to bridge SIP and RTP into the mobile network's SS7 infrastructure. In this implementation, the mobile handset continues to operate as it always has (as a GSM or CDMA based device), but now it can be controlled by a SIP application server which can now provide advanced SIP based services to it. Several vendors offer this kind of capability today.

Mobile VoIP will require a compromise between economy and mobility. For example, Voice over Wi-Fi offers potentially free service but is only available within the coverage area of a Wi-Fi Access Point. High speed services from mobile operators using EVDO rev A or HSDPA may have better audio quality and capabilities for metropolitan-wide coverage including fast handoffs among mobile base stations, yet it will cost more than the typical Wi-Fi-based VoIP service.

Mobile VoIP will become an important service in the coming years as device manufacturers exploit more powerful processors and less costly memory to meet user needs for ever-more 'power in their pocket'. Smartphones in mid-2006 are capable of sending and receiving email, browsing the web (albeit at low rates) and in some cases allowing a user to watch TV.

The challenge for the mobile operator industry is to deliver the benefits and innovations of IP without losing control of the network service. Users like the Internet to be free and high speed without extra charges for visiting specific sites. Such a service challenges the most valuable service in the telecommunications industry — voice — and threatens to change the nature of the global communications industry.

Technologies

Mobile VoIP relies on two main technologies:

• UMA — the Unlicensed Mobile Access Generic Access Network, designed to allow VoIP to run over the GSM cellular backbone

• SIP — the standard used by most VoIP services, and now being implemented on mobile handsets

Recent developments

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. Recently Nokia introduced a built in VoIP client to the mass market device (Nokia 6300i) running Series 40 operating system. Nokia maintains a list of all phones that have an integrated VoIP client here.