Mobile phone users are set to hit the 435 million milestone by 2012, driven by a growing acceptance of SIP by mobile operators and device vendors, forecasts Informa Telecoms & Media.

Sales of mobile phones with active SIP functionality will reach 275 million units in 2007, an increase from 0.4% of total device sales in 2006, to 19% by 2012 with a real inflection taking place between 2010 and 2011.

Within the mobile handset space, SIP is essentially split into two main variants of IETF SIP, also known as Naked SIP, and 3GPP SIP, which is also called IMS SIP.

IETF SIP is widely used in both fixed and mobile telephony and thus is an obvious choice to use as the basis of a convergence platform. In the mobile space, IETF SIP is considered to be an essential component for enabling access to open internet services including wireless VoIP.

“The lack of control over its development and its widespread use means that many mobile network operators perceive IETF SIP as a challenge to their business models,” said Malik Saadi Principal Analyst at Informa Telecoms & Media and lead author of Mobile Converged Devices: Enabling IMS, SIP, UMA&VCC services report.

The number of mobile users enjoying IETF SIP based services is likely to grow from 2.2 million in 2006 to more than 212 million in 2012. Malik Saadi says: “This growth will be mainly driven by the strong will of device vendors to get involved in the content space but also by the increasing number of new entrants among VoIP and internet content providers who are determined to challenge the mobile operator walled-garden service offering.”

3GPP SIP on the other hand is a mobile operator led initiative is designed to create an ideal ecosystem for them to leverage the potentials of IP without losing control of their walled-garden services‰ he continued. The number of subscribers who have embraced 3GPP SIP-based services did not exceed 1.15 million in 2006. However, mobile network operators‚ growing acceptance of SIP and their relationship with mobile handset vendors will see increasing numbers of 3GPP enabled devices produced. This, in turn with the availability of 3GPP SIP services such as Push of service over Cellular networks (PoC), Mobile Instant Messaging (MIM), Video Sharing and in the future mobile VoIP (mVoIP) will help grow subscriber numbers further. By 2012, the number of subscribers using 3GPP SIP based services will exceed 276 million, thus surpassing the number of IETF SIP service users.

In terms of devices, sales of handsets with active SIP were as low as 4 million units in 2006. Due to its high device requirements and the specification of services it will likely support, SIP implementation will be mostly limited to smartphones. Nokia enjoys the largest SIP enabled product portfolio of all leading handset vendors, which goes in line with the company‚s strategy to get increasingly involved in the mobile content space and internet service offering. Nokia has already release over 35 SIP capable devices among its E-Series and high end N-Series. It is important to note that sales of SIP capable handsets, which are those that offer plug-in mechanisms for embedding SIP, can be much higher than those of SIP-activated handsets, where SIP functionality exists and is activated.

For example, in 2007, sales of SIP capable handsets is expected to reach more than 33 million units whereas SIP is likely to be activated in less than third of these devices - almost 11 million units.