To check if a contact name already exists in the address book you could add...
public boolean contactExists(String contact) {
if (contact != null) {
Cursor cursor = getContentResolver().query(ContactsContract.Contacts.CONTENT_URI, null, null, null, null);
while (cursor.moveToNext()) {
if (contact.equalsIgnoreCase(cursor.getString(cursor.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME)))) {
return true;
}
}
}
return false;
}