This would depend on if the line is a stand alone line only being assigned to one extension or on a PRI having DID service. Do a Feature *0 and check the line buttons. It will show the line number or target line number. With this information you can check it in one of two ways. If it is a stand alone line and provided a line number, access the line by pressing the line and dialing your cell phone to get the Caller ID information. If it associated with a PRI having DID service, you will have to check the target line information in programming. A system administrator or vendor needs to do this.