The Charlotte Observer reports that USAirways is planning to delete accounts that have had no activity for 36 months or more unless something posts to the account by February 15.
According to the piece USAirways has not enforced its 36 month rule for several years, but plans to as part of the database cleanup involved in merging the America West FlightFund and USAirways Dividend Miles programs together.
Any activity is enough to keep an account active, but the activity needs to post by February 15.
You could always buy miles, book an award and redeposit it, redeem miles for magazines, or transfer points into or out of your account via Points.com (you could even transfer your points to America West and then transfer them back with no cost or devaluation).
(Hat tip to Today in the Sky.)