Modern interfaces in the phone, with all the bells and whistles, do not have enough integrity. If I made a phone, I would take a piece of paper and draw a sign. Horizontally and vertically all the functionality, point by point. At the intersection, how these two points integrate. For example:
Calendar + Contact in Address Book = Birthday Reminder
Photo + Contact in the address book = Mark a person in the photo
Calendar + Photo = Place photos, grouped by date
Photo + GPS = Location where the photo was taken
GPS + Contact in the address book = put the address of the contact, the address of his work, etc.
SMS + Contact = Arrange SMS as chat
GPS + Call Log = Show where the call was made, (doubtful, but may be useful for an alibi)
Notes + Contact = mobile CRM, leave any notes about the person, from the wishes on the DR ending with the fact that he owes 100 bucks (in any quantity and keeping the past)
Contact + Reminders = a reminder to call, call and make an appointment, come to the contact home, send an SMS. Or show a reminder when an incoming, with an incoming SMS from the contact
Reminders + GPS = remind what needs to be done when the phone is in a given place
Internet + Contact = friendfeed aggregation, rss from homepage
Internet + Music = last.fm
Bluetooth + Contact = Associate contact and bluetooth address, store transmission history, (or better yet, chat with SMS, call logging, broadcasts, rss, etc.)
SMS + GPS = Send SMS on arrival in the specified area. “Son, send sms how to get there”
And so on. It is so obvious that someone has implemented the thread or goes to it. It remains to find (wait) this phone and buy.
For clarity, a table of these starting points on docs.google.com