Yep, it's just a small box (like 1*3 inches?) that you hook up to your wireless router (alternatively, it can be inserted directly into your computer/notebook via USB; you actually call through your computer mic and speakers, but then you have to keep the computer on all the time; ). Both companies give you the option to select your own number (can be with any area code you want), change that number whenever(?) you want, or port your old number. Nettalk does it for free, Magicjack will charge you $20 one time + $10 every year(?) for that privilege.
The big advantage for me is that you can take the adapter with you if you go on vacation, assignment, etc. - and you have your "home phone" always available. Unlimited calls to US and Canada.
The phone has free features like caller ID, and I believe Magicjack will even send you the answering machine messages as audio files into your email - all for
$50 (box+1 year service) + $30 additional years for Nettalk or
$70 (box+1 year service) + $20 additional years for Magicjack.