Being on-call is generally synonymous with carrying a pager, physical or otherwise. Alertmanager, at the time of writing, supports four pager-style service integrations: PagerDuty, Opsgenie, VictorOps, and Pushover. The configuration for each of these services is fairly simple to get started, as they mostly revolve around API URLs and authentication tokens. However, they also support deeper levels of customization, such as adding images, and links, and configuring service-specific fields, such as severity. These advanced configuration options are described in Alertmanager's official documentation, so they won't be replicated here. The following example demonstrates a basic configuration for PagerDuty:

global:
  pagerduty_url: 'https://events.pagerduty.com/v2/enqueue'

route:
  receiver: 'default'

receivers:
- name: 'default'
  pagerduty_configs:
  - service_key: 'PAGERDUTYSQUADTOKENEXAMPLE'

Just like in the previous notifier, since the pagerduty_configs configuration is a list, you can trigger multiple service routes in a single receiver. You can find out more about PagerDuty's integration with Alertmanager here: https://www.pagerduty.com/docs/guides/prometheus-integration-guide/.