I work for Ritter Communications and we use the 4000 which services Marked Tree, AR Blytheville, AR and most neighboring rural communities. We have seen no degradation on our 4000.
I can account for the 4000 still being in State College, PA as of April 17, 2010 (although they switched from a small local company, D&E, to a national company, Windstream. Goodbye, WS4000. )
I work for Bledsoe Telephone in Pikeville TN we still use a 4000. sometimes I have to powercycle it because it will get stuck on the locals.