Default WL_CALIBRATION
It looks like most phones are very close to being calibrated already and I think the calibrations are already done in the touchscreen controller themselves.
For example the calibration for the htc ace:
ENV{WL_CALIBRATION}="0.963488 0.004947 14.422623 -0.076271 1.026566 -7.303467"
Is very close to a empty calibration:
ENV{WL_CALIBRATION}="1 0 0 0 1 0"
The formula from the calibration values is:
x' = Ax + By + C
y' = Dx + Ey + F
The relative big change in the third and last parameter is because those are in pixel values and those are quite close together on phones.
Maybe it's better to use the emtpy calibration for most phones instead the one copied from the mako while porting.