The two "Cingular" networks you are picking up are most like 310-38(0)
and 310-41(0).  One network is the former AT&T Wireless network, and the
other network in the old Cingular network.  They will, however, both be
integrated as time goes on.

A little analogy -- you have 3 employees: John (1), John (2), and Hans.  
When you ask for John, you automatically get John (1), even if you want
John (2), who may have more skills than John (1).  John (2) is leaving
the company, but teaching all his skills to John (1) before leaving.  In
the mean time, you may require John (2) for certain tasks or services.

This is very similar to the 3 networks of Cingular, Cingular, and
T-Mobile.  Even though Cingular and Cingular have the same name, and are
owned by the same company, they are still separate networks.  The phone
will be set to prefer one network over the other, as phones will always
prefer their home network over their roaming networks.  However, the
phones don't realize that Cingular and Cingular, while being different
networks, are the same company.  If you are ever in an area where the
second Cingular gives you better signal, don't hesitate to switch to it.

TH