This is not a 100 percent functional product. There are A LOT of flaws with the Nettalk Duo. This is a substandard product. That being said, I can live with the flaws for the savings it offers because I don't use a telephone all that often, and I mostly make out going calls.
Major Problems with DUO:
Device randomly stops working and you have to monitor it's 'green' light to make sure its on
Drops calls frequently
Incomming calls, often don't come in
Voice mail does not work if DUO is not plugged in or functioning in your home (which it doesn't up to half the time), which is a MAJOR flaw. I wouldn't mind its lack of functionality by half if I could get a voice mail when it wasn't working. However, when its not working, people who call me get nothing, not a ring, not a "sorry" message, just dead silence.
Minor Flaws
Voice distortion, many people complain that they can't hear me or I'm distorted when I talk on the phone
You have to dial the area code before every local number, or it won't work. No message telling you what you did wrong, and no instruction on this point with product, you just gotta figure it out yourself.
In summary, if you need a phone for an emergency, DO NOT get the duo. If you needed a reliable phone for receiving callbacks on jobs, or other important things, DO NOT get the duo. This is a completely unreliable, buggy product that practically requires a babysitter to make sure it works.
All that being said, I'm cheap and I don't use a phone much, so I'll live with it's MANY flaws for the substantial discount, however, I am at a total loss to understand why so many reviewers here defend this product so vehemently. It is NOT a quality product and NO ONE should represent it as such. While I can understand people like me who put up with its flaws for its price, I find it reprehensible to over-rate a product because you choose to put up with its lack of functionality. On this product it seems like a lot of people are sabotaging the integrity of the review process, which is why I felt so compelled to give a accurate product review. BUYER BEWARE!