Fixed and mobile network operators will invest more than $450m in capital infrastructure over the next five years to provide fixed-mobile convergence, market watchers predicted today.

A new study from ABI Research said that this investment is being made largely to ameliorate traffic migration to VoIP service providers, and lead to the implementation of more SIP-based services.

The research forecasts that operators will generate $97bn worldwide in service revenue from fixed-mobile convergence applications in 2011, mainly from offering lower fixed-line call charges to mobile users.

"Operators are seeing their core voice revenues come under pressure from VoIP, and they need to minimise call substitution," said ABI Research analyst Ian Cox.

"One way is to provide services over the broadband fixed network using a mobile device. Dual-use and single-use devices will be able to do that over Wi-Fi and micro cellular access points in the home and office."

Fixed-mobile convergence will reduce call charges when the device is connected to an indoor access point, and will allow the same device to be used everywhere with a single bill and contact list.

But although convenience and lower call charges are an attractive combination, Cox warned that call charges need to be "simple to understand, and dual-use devices need to be as appealing as single-use devices in terms of battery life, price and choice of models".

Fixed-mobile convergence will also allow continued development of SIP solutions for vendors.

SIP enables new services to be introduced quickly, and discarded if they are not popular. A single database holds all subscriber information, leading to lower operating costs for multiple services over multiple access technologies.