I am looking for a simple cell phone that is compatible with US
networks, preferably Cingular - will use a sim card.  It will be used
by an arthritic senior and must have big buttons and no features to be
accidently accessed.  The only features needed are the ability to make
and get calls.  I have not found anything, except in overseas markets.

I don't know about the SIM card feature, but you could try a
voice-activated cell phone designed for people with disabilities. 
Here's one company that says it works with Cingular (among other
providers):

http://www.etoengineering.com/quadriplegic.htm