To your questions -
Is it possible to make a call due to email? - do you mean trigger an Incident via email? If so, then yes with our email integration.
In that case, is it possible to switch the contact list and make a call depending on the content? - you can use our rulesets function to route particular events to a service. You can then create on call schedules for this issue specifically.
・ How many calls can be made at the same time? Also, please tell me the charge for increasing it. - Notifying people is based on the Escalation policy and the limits on escalation policies differ on the plan you have.
・ Is it possible to automatically wait for the same alert within 5 minutes? - Yes, we have paused incident notifications for this.
・ How many contacts can I register? -> 20 / person - 10 per person
・ How many contacts can be registered? - 20 per person.
Hope this helps clarify things, please let me know if not or if you have any further questions.