I'm having a doozy of a problem with my Photon right now. On the Evo 4G and 3D, I was able to install Handcent and the pop-ups worked as they should.
Now, for some reason on the Photon, I wasn't getting any text messages. I discovered it was Google's own Voice app that was causing it. To allow for text messages, I had to go and change a setting to notify through a text. A warning popped up stating that I'd receive two notifications. Sure enough, I recevied just that. The Handcent pop-up came back, but so does a GV notification.
This never occurred on my Evos... is there something I'm missing? I used the same exact settings in Handcent (I actually backed them up from the Evo and restored them onto this phone). I've uninstalled and reinstalled, but I can't seem to figure it out...