Take any calendar appointment on your phone (or make one) and add the email of the person you want to send it to as an invitee. It will email them a calendar appointment.
My work outlook even recognized it as a calendar appointment with the accept/cancel and adding it to the calendar etc.
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Oh, that looks like an exchange thing.
But anyway if you mail it to someone using regular imap or something and they view the email on their ios device they still get the email and because the phone recognizes dates and things in email it is just a tap on the date and select the create event or show on calendar options. That kind of works too though they might have to copy the notes out of the email before going to the calendar.
