I started using Net2Phone a few month ago, with their standard software. At first the quality of communication was not so good, but it improved tremendously over the following months, up to the very good quality it has now.
Sometimes connections don't work well (you can hear the person you call but he cannot hear you). Sometimes the quality is bad, but overall it works well.
I then used the embedded version of Net2Phone 'embedded in MSN Messenger), and it worked very well as well.
Recently, when I wanted to add funds to my account, everything went wrong, and Net2Phone asked for additional financial information (though I still use the Visa card I have been successfully for month), which I provided, and... nothing!! No mail from the Commcenter. I then joined the France helpdesk (very friendly). They confirmed, said that they could no nothing from the French helpdesk, that the US helpdesk did not answer their e-mails.
So I turned to another provider, slightly more expensive; they checked my Visa card within 48 hours (yes, the same one I use with Net2Phone), and the quality of sound is EVEN BETTER.
I think that Net2Phone grew so much over the passed months that they now have problem supporting the service and the customers
So my recommendation would be: use Net2Phone AND another provider

Recommended: Yes