Phones supporting voice over Wi-Fi are limited in numbers today but will exceed 100 models by year end. VoIP will be big; the number of Wi-Fi/cellular phones shipped incorporating some form of SIP voice support is forecasted to exceed 50 mln by 2011. Many of the issues with early Wi-Fi/Cellular handsets, such as limited battery life, will be resolved in models released during 2007, In-Stat reports.