Avoxi virtual call center may not be among top vendors in this niche, but it’s a very solid solution with great features. More importantly, it’s one of the few vendors that works outside US as well (in Jamaica, Costa Rica and South Africa). If you are looking for a free Avoxi alternative that can be used either as a call center or unified communication platforms, Bitrix24 is with worthy of your consideration. Especially since Bitrix24 is free for 12 agents, is available both in cloud and on-premise (with open source code access) and lets you rent toll-free and local phone numbers in 60+ countries.
* Please note that the information may have changed since the publication. For current prices and features please visit Bitrix24 pricing page.