Outbound Notifications & Alerts

PagerDuty by Andrew, Alex, and Baskar at Synchronicity Labs

is a tool to help manage on-call staff and set alarms to escalate
tickets through the appropriate channels. Forward alerts from your
existing monitoring systems (Nagios, RightScale, etc.) to Pager Duty,
configure your on-call schedule and business rules for escalation, and
PagerDuty takes care of notifying your team members.

Twilio, PagerDuty offers voice notifications in addition to their SMS
and email alerts. If you specify to receive an alert by phone, the
contents of the alert are read aloud and the call recipient has the
choice to suppress or resolve the ticket.