FaceTime fails with WiFi Connection Lost iPhone 4

My Google skills havent found any matches for this, but perhaps others have seen it in passing at least.
Ive noticed recently that Ive been having problems with FaceTime calls to a friend of mine. For the past month since he got his iPhone 4, hed end up losing the WiFi connection, but now its happening to me, too.
The symptom is that the FaceTime call will be going fine for a while, and then it will just hang with no motion in the picture from the other phone for about 10 seconds, then the phone will beep and display this error:
FaceTime Failed
WiFi Connection Lost
<OK>
At this point, I find that my WiFi indicator in the status bar is gone and replaced with 3G. It has indeed lost its connection to the WiFi access point (a Time Capsule).
Going into the iPhones settings, I see that it shows there that it is still connected to my WiFi network (showing a checkmark next to my WiFi network name, although it still says 3G at the top). Cycling WiFi off and back on corrects the problem.
My friend is also using his iPhone 4 connected to a Time Capsule, so we have similar setups. Im beginning to wonder whether theres some problem either in iOS 4 or the Time Capsule that causes the wireless connection between them to disconnect in an aberrant fashion.
So, anyone else seen or heard of this?
iPhone 4 iOS 4