Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Flowroute - Flowroute provides direct access to telephony resources - such as calling, messaging (SMS & MMS), call routing, SIP Trunking and Communication APIs.
LiveAgent - LiveAgent is a fully-featured web-based live chat and help desk software. It harnesses the power of a universal inbox, real-time live chat, built-in call center, and a robust customer service portal. Start your free 1 month trial today!
Tatango - Tatango is a mobile messaging platform for agencies.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Postscript - Like Mailchimp for SMS