Like others on this forum I use both. I use the 9700 for all text messages, email, sms etc. I also use it as a camera as the iphone camera is a POS.
I use the iphone for the other tasks, games, music etc..
I will step back to one device when a viable machine with a full screen and real keyboard is available. The HTC Dream is close . . . maybe the Dream II . . . . . ?