Lagging here, too
I have a 16 gig iPhone 3G with the 3.0 upgrade. Mine is lagging, too.
But I don't Text. Peggle seems to make the lag worse for me.
Apple and PopCap blamed each other.
Two weeks ago, the Genius at the Apple Store told me there was nothing wrong with my iphone with lagging. He blamed it on having too many apps and the need to reboot more frequently. He told me to go home and restore and see how it worked with fewer apps. Still lagged.
I started a thread here to ask how often everyone rebooted their phones, but no one seemed to have the same problems I was. Someone suggested getting an app to free up the memory, but I thought that I would just turn it off more frequently.
Two days ago, my iPhone would not turn on at all. (Not related to the lagging, AFAIK) The Apple Store replaced it - no problem. (And I'm happy to say that I have no dead pixels, no dust under the screen and no light leaks in the replacement either.)
The sad news is that my replacement iPhone is still lagging.
Is it in 3.0? I was considering restoring back to the old software to see if that helped get rid of the lag. I will let you know how that goes.