I have the iPad2 and an iPhone 4, I don't really think you need the 4s with the iPad, if you want an iPhone maybe just wait for the next one.
Yup, that is exactly what I am doing. iPad 2 is more for video and browsing, while the iPhone 4 is for music, podcasts, and quick jumping on the web.
Both devices cover all my bases. I'll wait for the next iPhone after his at least, as well as what, an iPad 4...
I just got my wife a 3GS, because she wanted the free one. In a year when I get whatever my next phone ends up being, she will get my iPhone 4, and I may take her 3GS, put it in the car, and use iTunes wifi syncing to load it up and change music selections, and it will never have to leave my car.