Fonality is offering software it says lets small and mid-sized businesses make free voice over IP calls.

Trixbox Pro is free software based on the open-source Asterisk private branch exchange software.

Up to 20 employees can use the software, which runs on any computer and nearly any phone, including IP and analogue models, said Chris Lymon, CEO of Fonality.

An Enterprise Edition upgrade for $9.99 per employee per month will provide some business features such as conference bridging, and a Call Center Edition, which is designed for the performance needed for use in a call centre, at a price of $19.95 per call centre agent per month, he said.

TrixBox launches with TrixNet, a free in-network calling service to let any TrixBox Pro user call any other TrixBox Pro user, using their regular phone numbers, Lymon said. TrixNet will be extended in the near future to TrixBox Community Edition, a popular open-source software based on Asterisk.

Fonality has 100 employees and has seen about 1.4 million downloads of TrixBox CE in the past two years. Lymon estimated there are about 2,500 customers in 50 countries for various Fonality products.

The arrival of Trixbox Pro gives an even greater advantage to open-source enthusiasts, Lymon said, even though open source is still a small component of total VoIP calling. "It's totally ready for telephony, and you don't even need to know about Asterisk," he said.