Google calendar
Basic enough is google calendar...you can partially share your calendar with anyone as long as you have their email...Accordingly you can manage this calendar on your iphone...I've using this systems for a long time and i works like a charm...
Of course the number of people you want to share the calendar with is relevant, but even so it's always possible to have a separate professional calendar, so it won't get overwhelmed...don´t forget the calendar should be your hard landscape, always keep it trustworthy and limited to appointments that are really!!! going to take place on that specific date and time!
You can put the link to the calendar on your site, which is really easy to extract from google calendar settings.