Can an iPhone app call another app?
<p>Example:  "Contacts" in iPhone does not organize contacts into groups (mailing lists).  You could write an app that maintains a database on the phone itself.  Groups could be "Co-workers", "Party friends", "Relatives" etc.</p>

<p>From another app it would be nice to call up this app.</p>

<p>Imagine an app named "TellMyFriends".  This app can summon the Photo Library to select a photo, or the Camera to take a new photo.  (You can do this with the iPhone SDK.)</p>

<p>Now you want to send the photo to "Party friends".  You want to summon the second app that has the database of groups.  Select the "Party friends" group and it returns with a list of names that the first app can then find in the phone's address book.  Can this be done?</p>
