I don't know all MTs, but I'd say you'll just lose contacts outside of your SIM card, right? contacts can be stored a) on the SIM card (factory reset does not affect) b) in the phone memory (factory reset clears) c) on the phone memory card (there it depends on whether the factory reset also formats the memory card, which I doubt ) and synchronous replicas, which should remain after the factory reset, but frankly, it has happened to me several times that they have been synchronized to irreversible d) on the cloud (google or samsung account, etc.) e) on PC (outlook, nokia, etc. .) In addition to those contacts on the SIM card, I would like to note that as far as I know, they only have a primitive structure and if they seem to be deleted, it may be because the mobile phone is in the default state after a factory reset.