Sprint, yes.  ATTWS, sure.  Cingular, think so.  Verizon, no.

There are some groups that have discounts.  Your ability to find that group
may be tough, and to blend in that group will be challenging.  I've heard of
a few that have crashed the "special" group for the discount, yet I am still
retail on Verizon.  And since I have a no-roaming single rate West plan,
there is no where else to go for that plan.  My city lines are on an ATTWS
Army foundation.  think it's 15% discount, but it may be 10%.  Call them if
you have interest.