Can we schedule SMS to be sent to custom contact list ? If so,please guide through the open available options
You need to retrieve the Phone Numbers on the extensions . Check the following reference: : https://developers.ringcentral.com/api-reference/
One way of doing is calling the create SMS API from your code using a scheduler . If you are using Java, you can use a Task scheduler or timer to call the API periodically. It is also possible in c# I believe.