Non-Alphanumeric Pagers are added as a contact method under the Email type on your profile page. When adding the email address, you will want to check the option to "Send Short Emails".
If you have a non-alphanumeric pager, you have two options for using it with PagerDuty:
Only use the pager for PagerDuty notifications.
Make a note of the numbers PagerDuty sends notifications from.
PagerDuty isn't able to send any information to a non-alphanumeric pager, so you'll need to configure a secondary method in order to acknowledge, resolve or find out more about incidents.
With an alphanumeric pager, you can enable short emails to receive information about an incident; however you'll need to configure a secondary method in order to acknowledge or resolve incidents.