I haven't looked into it at all yet. I only see or hear of it on TV ads. I have always been leery of things on TV ads. No matter their claims. But that's just me. The original skeptic.

Yes, I tried MagicJack -- wait for "MagicJack Plus"
 

I tried MagicJack perhaps a year ago, and returned it for a refund within 30 days, for only three reasons:
1. the only (my choice of available area code/exchange) provided phone #
was long distance from my physical location,
2. I had to have my computer on (and running MagicJack software) at all times, when I wanted full phone service. (Only Voicemail when not running their software).
3. Everytime I booted my computer, the revised software was Downloaded/installed (great the first time, but why do
it again when it had NOT again changed?).

MagicJack (almost always) had fine sound quality.

I recommend you WAIT (perhaps 3 Months) for
"MagicJack Plus."
See short article @ PCWorld website(respected magazine),
"PCFree MagicJack Coming Soon", Jan-08-2011,
or just Google on "MagicJack Plus".

"MagicJack Plus", alleged to be coming by April 2011;
$50 for device & 1st year VoIP service ($20 each additional year). Do NOT need to run a pc to have full phone service!
(I feel this makes it fully competitive with SkyPE & Vonage, but much cheaper re United States phone service!)
Just connect included device to AC-outlet,
set up WiFi/4G-adapter/Ethernet connection,
and connect a regular telephone to its RJ-11 port.
(I believe I can perhaps live with
its having a non-local phone #,
and its doing one download
each time I plug it into an AC-outlet.)

I have magicjack and just love not getting bills in the mail. I have had it for a couple years it is 19.95 a yr. I know it has some quirks but all in all its great I wouldn't go back to regular phone and 100.00 phone bills for nothing. I can put up with a little when the benefits are so great.