I'd bet it'll be some months unless there are some crazy good numbers. There are probably only hundreds of thousands at most, more likely 5 digits. There's plenty of chatter on the internet from people who preordered, but I have no idea how many others are silent. Honestly I'd figure most people who preorder this phone are the talkative type, which means that sales could be lower... (since there aren't 100k+ people claiming to have it on the way).
I suspect that this phone will have strong sales over its life, but only after the marketing gets underway--many people didn't really pay attention to the phone until this barrage of media reviews as it were. Plus there aren't enough WP7 faithful or jaded iOS/Android users to pump the preorder numbers super high.
It'll do well, but it'll take time and lots of tlc.