Why does my Samsung Sprint phone drop from an excellent signal to dropped
call to Digital Roam and back -- all within, say 15 seconds while sitting on
my desk at home in "Speaker" mode without anyone touching it or moving in
the same room?

Is this a phenomena unique to Sprint?

I've called their support and the answer is "You shouldn't have that
probelm" but no expanation.

I'm in Brooklyn, NY.

I also notice Digital Roam popping up in midtown Manhattan (38th and
Broadway, for example), crossing the Manhattan Bridge on the Subway and
other unexpected places.

Is the coverage that bad?

If so, anyone have any suggestions as to a more reliable carrier within New
York City?

Cheers,
Jim