The iOS Native Apps internally uses .sqlite database to store the information for most of the Apps managed through CoreData Framework (Similar to EDF for .Net).
If you want to explore or backup these files you can access them from a RAW filesystem using iFunBox. If you have jailbroken device then you can use the iFile App to manually backup these files.
iPhone Contacts :
Path : /private/var/mobile/Library/AddressBook/AddressBook.sqlitedb
iPhone SMS messages :
Path : /private/var/mobile/Library/SMS/sms.db
iPhone Native Notes :
Path : /private/var/mobile/Library/Notes/notes.sqlite
iPhone Call Logs :
Path : /private/var/wireless/Library/CallHistory/call_history.db
Few More Hacking :
1.You can use this path to automate few things. Example : You can read this file and initiate a email whenever you miss a message or call by simply querying this db file.
2.Its dangerous to write any changes to this file as this controlled by CoreData. So, its recommended only for read purposes.
Thanks for reading.