NAGIOS notification command for service/contactgroup

We have 3 templates for services, low-priority, high-priorty and medium-priorty. Low priority services are attached to the contactgroup low, medium priorty services are attached to the contact group medium and high priority (OK you probably get the idea).

Low priority services don't notify, medium priority alerts notify by email and high priority alerts notify by email and phone. Except they don't (yet)

What I need to do is specify that any alerts generated by high-priorty services should run the notification commands notify-service-by-email and notify-service-by-phone. From reading the documentation (and my knowledge of Nagios) the only way I know to set notification commands is the service_notification_commands option in a contact, but that would mean each contact would need two definitions, one for phone and one for email. How would I get high-priority services to call the notify-service-by-phone command?

More info;

Service Templates

;High priority service (Alert by call, 1 min check period)
define service{
    name                high-priority-service
    notifications_enabled       1
    normal_check_interval       1
    contact_groups                  high
    use             generic-service
    register            0
    }

;Med priority service (Alert by email, 5 min check period)
define service{
    name                med-priority-service
    notifications_enabled       1
    normal_check_interval       5
    contact_groups                  medium
    use             generic-service
    register            0
    }

;Low priority service (No alert, 10 min check period)
define service{
    name                low-priority-service
    normal_check_interval       10
    use             generic-service
    register            0
    }

(generic-service is the default template from NAGIOS configs with a few tweaks)

Services

define service{
        use                             high-priority-service
        hostgroup_name                  generic-server-nrpe
        service_description             SSH
        check_command                   check_ssh
        }

Contact groups

define contactgroup{
        contactgroup_name       low
        alias                   Low Priority Notifications
        members                 sam,[...]
        }

define contactgroup{
        contactgroup_name       medium
        alias                   Medium Priority Notifications
        members                 sam,[...]
        }

define contactgroup{
        contactgroup_name       high
        alias                   High Priority Notifications
        members                 sam,[...]
        }

Contacts

define contact{
        name                            generic-contact
        service_notification_period     24x7
        host_notification_period        24x7
        service_notification_options    w,u,c,r,f,s
        host_notification_options       d,u,r,f,s
        service_notification_commands   notify-service-by-email
        host_notification_commands      notify-host-by-email
        register                        0
        }

define contact{
    contact_name    sam
    use             generic-contact
    alias           Sam
    email           sam[...]
    address1        +44[...]
    }