As far as I can tell, only three bloggers participated: Ed Morrissey, Jazz Shaw (who writes at a blog called The Moderate Voice), and James Joyner. According to Joyner, "... we were apparently the entirety of the audience," though he also noted, "a couple of others joined in during the call."
Morrissey and Joyner, of course, are both respected conservative bloggers. I'm unfamiliar with Shaw, but that probably has something to do with the fact that his blog is called The Moderate Voice. In any event, these three seem like fine bloggers to invite.
It is unclear why the three bloggers were chosen, but it probably wasn't because they are viewed as being "pro-Barr." Though Shaw's comments were generally favorable, Joyner's blog post about the call notes that: "(Barr) is likely to take away votes that would otherwise go to John McCain, making him essentially an Obama stalking horse." Still, the sentiment of the bloggers seems to be that Barr is a much more presentable messenger of Libertarian philosophy than Ron Paul.
In any event, it is curious that Barr would hold a conference call and not invite more bloggers. As Morrissey wrote in his post, the call invitation noted that: “Bob Barr loves bloggers, [and] values your role in informing the public" ... But it appears Barr loves some bloggers more than others. Don't get me wrong; I don't feel that I have to be invited on every call -- but where was everyone else??? ... Or were other invited bloggers just so disinterested in the call that they didn't bother to dial-in? Either way, it doesn't seem like an effective "New Media" strategy.
Update: I should note that the Barr campaign was kind enough to grant me an extensive interview on the day he announced. You can watch it here.