I don't know how far down the PR track you've gone, but if i may  
indulge in some unsolicited advice based on experience I'd say:

Nothing else beats the hard graft of working through a list of press  
contacts in terms of getting attention. Decide what the audience you  
want to reach is and work out your message(s) accordingly. You need  
to give the journo an angle - one of the oldest tricks for product  
announcements is to present the results of a "survey" that proves  
there's a problem, that your product magically happens to solve!  ;-)

Anyway, there's stacks of stuff on the web about this sort of thing,  
so read widely, check out some media releases from existing  
companies, etc. and synthesise your own plan from there.

Finally, make sure that you have a spokesperson that can be reached  
on the phone during biz hours, journos working to a deadline will  
more likely pick up the phone to get a fast answer, not wait around  
half a day for an email reply...