I've seen it also, with my Verizon phones. It's not limited to the Mogul, nor to WM based phones. It's a network problem that has always defied solution. Fortunately, we haven't noticed it for a long time.
For what it's worth, we've never seen it with SMS from one Vzw phone to another Vzw phone. When it's happened, it's been when sending to Vzw phones from email via the
nnnNNNnnn@vtext.com route.
- Tim