Yes, Text Chat can be built using our messaging technology which is included in the OpenTok platform. 10 million signaling messages are included in the basic subscription of $50/month, and are priced at $1 per 1 million messages/month thereafter.
The OpenTok iOS Text Chat component provides code for adding a user interface component for displaying and capturing text chat messages in an iOS & Android application. The component is currently available as a beta version.
To start building text chat from scratch see our technical documentation here.