Dual-Mode/Multi-Mode Handsets require a mechanism to switch between networks for seamless call continuity. This article introduces the concept of dual-mode calls and the challenges of integrating software on the handset to implement handoff and services for VoIP using IMS infrastructure. Included
is a solution Hellosoft has designed for easy adoption and addition of IMS/VCC services.

Reprinted in its entirety from ARM IQ Vol. 6, No. 1, 2007