Big thanks to Xummoner for sharing this information to the Motomodders.net community:

1. Telnet to ezx_user/download/appwrite/setup and open a file called ezx_addressbook.cfg,
2. Check the line where it says "NUMBER_MATCH_MINLEN = 11" pay attention to the "MINLEN" part. Change the value from 11 to 7 (or whatever length your short phone numbers are without area code). You can use VIM to edit directly or you can also download it to your computer, edit it with wordpad (or any text editor) and then upload it to the phone replacing the original one
3. After that, turn off your phone, turn it back on and voila! Every new message or call should be properly recognized by the phone.