3CX is a software-based PBX solution with a cloud hosted option, offering users web conferencing, CRM integration, instant messaging, and native mobile apps.
AT&T is a US-based telecoms company, and the second largest provider of mobile services and the largest provider of fixed telephone services in the US.
Microsoft Teams is a chat-based workspace in Office 365 which lets users collaborate on documents, make voice & video conference calls, view chat logs, and more.