On the subject of contacts: while these can be copied from the SIM the data are not used from there. They are stored in a database on the phone. A contact can be either just recorded in the phone’s database or associated with an account (such as gmail) so that it can be synchronised for backup and if required, transferred to another phone through the account. There have been problems in the past with phone-only storage.
See other posts here.
The SIM is no longer a solution for storing or transferring contacts, there are better solutions such as synchronizing or .VCF file. Also the SIM will only store a name and a number, nothing more.
On random reboots there’s a lot to read too.