Write this piece of code in navigation controller.m:

ABAddressBookRef addressBook= ABAddressBookCreate(); // this will open the AddressBook of the iPhone
CFArrayRef people = ABAddressBookCopyArrayOfAllPeople(addressBook); // this copies all the contacts from the Address Book into the array
NSString *contactName = [[NSString alloc] init];

// specify the contact name to be edited
contactName = @"ABCD";
for (int i =0 ;i<ABAddressBookGetPersonCount(addressBook);i++){
ABRecordRef ref = CFArrayGetValueAtIndex(people, i);
NSString *firstName = (NSString *)ABRecordCopyValue(ref,kABPersonFirstNameProperty); // this gets the First Name of the person

// check whether the editable contact exists in the AddressBook if exists then allows the user to edit the contact
if ([contactName compare: firstName] == NSOrderedSame) { 
ABPersonViewController *personController = [[ABPersonViewController alloc] init];
personController.addressBook = addressBook; // this passes the reference of the Address Book
personController.displayedPerson = ref; // this sets the person reference
personController.allowsEditing = YES; // this allows the user to edit the details
personController.personViewDelegate = self;
personController.navigationItem.rightBarButtonItem = [self editButtonItem]; // this will add the inbuilt Edit button to the view

// this displays the contact with the details and presents with an Edit button 
[[self navigationController] pushViewController:personController animated:YES]; 
[personController release];
} 
}


// setEditing method needs to be overridden for edit functionality to work properly
------------------
- (void)setEditing:(BOOL)flag animated:(BOOL)animated {
[super setEditing:flag animated:animated];
if (flag == YES){
// change the view to an editable view
[ [self navigationController] setEditing:YES animated:NO];
}
else {
// save the changes and change the view to noneditable
[ [self navigationController] setEditing:NO animated:NO];
}
}

- (BOOL)personViewController:(ABPersonViewController *)personViewController shouldPerformDefaultActionForPerson:(ABRecordRef)person property:(ABPropertyID)property identifier:(ABMultiValueIdentifier)identifierForValue {
return YES;
}