3CX - Hosted PBX with CRM integration and mobile apps
Grasshopper - Grasshopper enables entrepreneurs to build a virtual office that connects callers to employees, wherever they are.
CallHub - Predictive Call Center, Voice and Text Broadcasting app
Ooma - Ooma us a free internet based phone service the delivers the efficient VoIP services at clear calls.
Asterisk - An open source telephony switching and private branch exchange service for Linux.
Voiceably - Voiceably is the provider of a local phone number to establish an independent cloud call center or business phone system.