I have had one since about October last year, was about to buy a Samsung B2700 when I saw the 3720 just after it came out.
The mobile network here is basic, no internet etc, but general phone functions work well and the reception in poor areas like inside metal buildings, is much better than either my previous old Samsung Solid M110 or my old Nokia 6230.
it has been a bit wet in an outside pocket on my flotation suit (though not fully submerged) but the charging socket is not plugged with anything so I don't know whether it would survive full submersion like a Sonim XP3.
Dropped it a few times, no problems.
The first signs of scratching are appearing on the screen, but I'm not that careful with it and occasionally it goes in a pocket with a bunch of about 20 keys which is not that sensible really.
I like the user interface (the Samsung's was crap) it is easy to use like most Nokias, the 2MP camera is fine for opportunistic use (I have a real camera when I am going out to take proper photos) but in bright colour conditions it can saturate easily - I have some photos with my orange Humber in where the colours are a little odd! Not great in low light as you'd expect from a tiny lens, but not bad. It has quite a decent torch on it, it's no LED Lenser but for a phone torch, not bad. The FM radio is pretty poor and speaker volume is a bit limited.
Mine came with a free 1GB memory card (ie loads of room for photos and ringtones) and it talks to both my Parrot car handsfree, and to my PC's Bluetooth dongle, neither of which the Samsung would do properly.
Criticisms - the ringtone could be a bit louder (easily drowned out by a carbed 115hp 2 stroke and 30 knot slipstream!) and like the vast majority of phones where the speaker is on the front/back rather than on the side, if the speaker is firing into your leg when you are sitting down, you don't hear it ring at all.
It isn't anywhere near as physically tough as a Sonim and doesn't do the "SAS walkie talkie look" at all, but from what I hear the Sonim electronics seem to break quite a lot anyway, and the price of those is a bit silly. My requirement was for a Nokia which was a bit tougher than average, reasonably well specced, and at a sensible price, and it fits the bill nicely. I'm not sure whether it would survive a decent salt water immersion but it's certainly much better than a normal phone. If I dropped it in the oggin I'd certainly buy another one.
A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
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