Information about usage of configured notification preferences based on escalation policy step/action:
- "notify selected group member" and "Notify group member from selected calendar" - one user is chosen and notifications are sent according to notification preferences (to all addresses with specified delay)
- "Notify all group members" - only the very first notification address is used
- "Assign alert to" and "Notify also" users at the very end of the escalation policy are only notified using the very first notification address
There is currently no possibility to limit the SMS contact usage. The contact preferences are used as described above. To achieve your scenario, you need an alternate user with only the SMS contact.
You can fill feature request on Alert Central Feature Requests page.