I didn't care for the first one; it was competently made, but too derivative for my liking, along with multiple endings, the final one of which didn't seem to make sense. There was a funny line in this movie as some characters recalled the events of the first one and asked "how did that end?"
In the first, there was a chain of deaths linked by cell phone calls apparently originating with a death in a home involving Munchausen Syndrome-by-Proxy. The deaths typically involved some sort of poltergeist activity preparing a location for a death by falling, and then a person being dragged or thrown from a height. Some of the deaths involved twisting of the body in bone-cracking ways. One clue found on the bodies is a red candy, and each call is announced by an annoying ringtone taken from a children's television show (one that exists in the world of the movie).
In this one (I might have called it Two Missed Calls rather than One Missed Call 2), the manner of deaths, and clues and possible cause are mixed up somewhat. The two female leads are quite attractive. Again, I guess it could be said that it is competently made, but I didn't find it very interesting and again the ending involves some sort of twists that aren't particularly appreciated. Those who liked the first one a lot might enjoy this one too. The first one is being remade and I would guess that a sequel will be made to that one as well though it will probably not be a remake of this one (think the American Ring 2 or The Grudge 2).
There's a short film "gomu" on the second disc which takes place in the One Missed Call world, though when in relation to the two films, I'm not sure. It is poorly shot on video and isn't really worth the minute or two that it lasts.