The Impression is larger and has a hardware keyboard. Those 2 factors set it apart from the other phones you mentioned. It also has a much more vibrant display. The Eternity has a somewhat stronger feature set than the Solstice, including a mobile digital TV tuner. We have reviews of all 3 phones on our site:

http://www.mobiletechreview.com/phones/Samsung-Solstice.htm

http://www.mobiletechreview.com/phones/Samsung-Impression.htm

http://www.mobiletechreview.com/phones/Samsung-Eternity.htm

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