Twilio - Brings voice and messaging to your web and mobile applications.

Softros LAN messenger - LAN messenger for an internal office chat for home or business users. It does not require a server and is very easy to install and use. It supports personal chats, group chats, message brodcasting, files transfer and remote desktop access.

Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates

MyChat - Secure instant messenger for any network

Clockwork SMS - Clockwork is an Easy Text Message API. An SMS API for Developers. Build powerful apps and include SMS. Signup is free, Try it now.

BORGChat - BORGChat is a LAN messaging software program.