I feel your pain... I've used Motorolas, Blackberries, and most recently a Nokia 5230, and voice dialing is definitely a feature that I miss on my N900.

However, I temper that loss by the acknowledgement that the N900 is more computer than phone. I bought it because I got a killer deal on it, and it does so much more than the 5230 does, and it leaves my old BlackBerry Curve in the dust. But its the secondary phone functions that sorely lack - conference calling is a bit different to use, call waiting requires a menu selection. Don't even get me started on the difference in Ovi Maps!

Back to the question of voice dialing... I've seen other threads here on TMO lamenting the missing voice dialing. Without having a home-brewed voice recognition and/or voice synthesis library, an open source voice dialing program is going to be near impossible - the voice recognition tech would need to be licensed, and that would be major money that probably couldn't be reclaimed with a free or low-cost program.

My solution? Low tech in the extreme: whenever I go on long driving trips, I bring the 5230 along for voice dialing and sat-nav. When I get to my destination, the SIM goes right back in the N900.