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PhotoDude,
The curves for Grey Gamma 1.8 and Dot Gain 20% are very similar (click on the 51 step tablet plot of assigned profiles attached - higher numbers are lighter, 0=black, 255=white). He selected it because it looked right to him on his uncalibrated laptop (Again, chances are it's a Mac or something set to look like one).
When you got the image file, it looked wrong because your gamma is probably pretty close to 2.2. So the same numbers look darker and more contrasty. If he had selected 30% dot gain, it would have been mostly parallel to your gamma 2.2, and a little lighter looking on your machine (it seems counter-intuitive, but that's how it is), except for the dark grey values, which would have been a bit merged on your machine. Watch that you don't lose low value separation in this scenario.
A friend often sends me files to print on my inkjet that are in the dot gain 20% space because he had gotten the scans made by a service bureau, which assumed a roughly default press rather than an inkjet. I do the same thing you did, and yank up the curve and then apply some other image-specific adjustments. It works fine, as you've experienced. Oh, and if he doesn't send me dot gain 20%, then it's grey gamma 1.8 (he uses a Mac), so, again, I have to adjust accordingly.
Glad you used the phone and everything worked out well.
Aloha,
Aaron