question

Hi there, 

Apple Calls this functionality " Guided Access"

You can use Guided Access to:

• Temporarily restrict your iOS device to a single app
• Disable areas of the screen that arent relevant to a task, or areas where an accidental gesture might cause a distraction
• Disable the hardware buttons

Here is a link to the Apple Support article on the subject: 
https://support.apple.com/en-us/HT202612

I would say probably, yes.  Google something like 'iPad kiosk mode' to see how to lock the iPad down to a single app.  Then I would consider putting the RingCentral user in a special role where everything is restricted except internal dialing to avoid potential abuse.