I think your decision should be based on two points. First, do you believe you have an immediate need/practical use for an iPad? And two, would the inclusion of features likely to appear in iPad v2 make you regret your purchase when v2 is announced?
In your situation, an iPhone 4 may negate the 'immediate need' of an iPad until a second version is released. Sure, an iPad still has many advantages over even the newest iPhone, but being able to play with Apple's 'newest' technology could be enough for now. You're getting iOS 4 with the newest bells and whistles, that alone would be enough for me.
As far as version 2 is concerned, consider what features are likely to headline the next iPad. Obviously no one knows for sure, but you can speculate. In my mind, iPad 2 will come in 32, 64 and 128 GB versions, will have more RAM (possibly 512 MB, like iPhone 4, or maybe more), a better graphics card, and a camera with FaceTime capability. Of course, I could be way off. What you should do is decide if features like these are worth waiting for. If they are, you should also consider whether you're willing to forego another seven months without an iPad, if you think you have a need for it.
Hope this helps.