Is there a way to tell Nagios which contact is standby?
For example:
-> There are 3 admins. Every admin is standby for a month (admin A: january, admin B: february, …). When a critical event occures, nagios has to check who’s standby and notify the standby contact.
You could pre-define 3 contacts with the same settings except for the email addy or whatever you are using to make contact.
You would then have to MONTHLY change the contactgroups.cfg file and add/remove members to the members directive for the contactgroup_name defined in the services.cfg file.
and this could be done by a script running on cron.monthly 
Luca