I don't think any Blackberry offers voice dialing directly - I'm not sure about the Nextel phones, since I've never used one. AT&T has a service where you dial a 3 digit number (#323, I think) and it then lets you dial by voice. Costs around $3 or $4 per month.

As for the range on the BT200 -- sorry, I did not get the chance to test this out. But take a look at the Jabra web site, and do a quick google search -- I'm sure I've seen lots of discussion around BT range and line of sight issues. Sorry.