Don't know if this is your problem, but this is what fixed my problem.
http://www.blackberryforums.com/gene...wer-cycle.html
---Update Saturday AM ----
I take it back. Some time after I made this post he stopped receiving his texts. Not only that, but the problem has not affected my phone that was receiving texts on Friday morning but no longer does unless I power cycle. This is clearly something larger than sending service books or making a setting change. Nextel has screwed something up here.
Roveer