To understand cloud telephony first we need to know about the requirements to implement cloud telephony and understanding where it can be implemented. Cloud telephony is the name given to multi tenant structure having multiple users sharing the resources at the same time. Unlike VOIP telephony this technology doesn’t require a dedicated hardware to be installed at user premises.
In other words you don’t require any hardware to route your calls, this can be done by API’s designed and developed by vendors interacting with web apps developed by user to give specified instruction for performing specific action every single time.
You need a dedicated number from cloud telephony provider or Telecom provider along with certain number of ports to route the incoming / outgoing calls to and from this number. When a call is landed on your dedicated phone number the vendor API interacts with user web application interface. This web application interface has a specific set of commands to perform predefined actions (playing text file, send SMS. Record etc)
Cloud provider performs the action mentioned under user Web App to every call received on dedicated number. Feature like auto scaling also comes handy to manage high peaks and decrease in call volume. Another feature of this technology is to pay for only what you have used, your data is secured as vendor mostly does not know anything about your application and they do not store your data with them.
Languages commonly used and supported by Vendor API’s are PhP, Python, Java, .net Ruby on Rails etc.
Using these languages users can easily develop the set of instructions to be performed every single time.