The SIDH (System IDentification for Home System) in your cellular telephone tells the cellular system what cellular carrier your cellular service originates from. This is used in roaming (making cellular calls when in an area not served by your cellular provider).

Every geographical region has two SIDH (System IDentification for Home System) codes, one for the wireline carrier and one for the nonwireline carrier. These are the two companies that are legally allowed to provide cellular telephone service in that region. The wireline carrier is usually your local telephone company, while the nonwireline carrier will be another company. The SIDH for the wireline carrier is always an even number, while the SIDH for the nonwireline carrier is always an odd number. The wireline carrier is also known as the Side-B carrier and the non-wireline carrier is also known as the Side-A carrier.

SIDH is often abbreviated to SID.

A list of SIDH’s can be found at http://people.ku.edu/~cinema/wireless/Cellular_SIDs.html.