Smooch.io for WhatsApp - Engage with your customers on WhatsApp like never before
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
WhatsApp for LiveChat - Let your customers reach you via Whatsapp
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
WhatsApp Chat for Shopify - Convert website visitors into customers with WhatsApp Chat
Sipdroid - Free and open-source SIP/VoIP Client