a.k.a. SIDH

SID means System IDentification, a number assigned to each cellular carrier in a different region. That does not mean that all offices of a particular cellular carrier will have the same number. Cellular One of Boston has a different SID that Cellular One of Buffalo. The FCC divided up the country into different areas, roughly the size of a city and its suburbs, and handed out licenses for two cellular providers in each area. WIRELINE SIDs will always be even, NON-WIRELINE SIDs will always be odd. A related parameter is the GID. If you don't know the SID of the cell you're in, it is possible to Read it with a Motorola phone. There's also a somewhat-outdated list.