How to use sqlplus to connect to an Oracle Database located on another host without modifying my own tnsnames.ora
sqlplus user/pass@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(Host=hostname.network)(Port=1521))(CONNECT_DATA=(SID=remote_SID)))


Maybe, and this might be dependant on the command line environment you're using, you need to quote the string, something like 

 sqlplus "user/pass@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(Host=hostname.network)(Port=1521))(CONNECT_DATA=(SID=remote_SID)))"


or

 sqlplus 'user/pass@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(Host=hostname.network)(Port=1521))(CONNECT_DATA=(SID=remote_SID)))'