Orbtalk have a range of SIP trunk products that work with the Avaya IP Office
IP Office is a highly modular IP telephone system designed to meet the needs of home offices, standalone businesses, and networked branch and head offices for small and midsize businesses. The award-winning IP Office gives growing companies a complete solution for telephony, messaging, networking, conferencing, customer management, and unified communications.
IP Office is a versatile communications solution that combines the reliability and ease of a traditional telephony system with the applications and advantages of an IP telephony solution. This converged communications solution can help businesses reduce costs, increase productivity, and improve customer service.