It definitely isn't possible now, and I wouldn't expect it in five years either. If you look at [1], you can see the areas of the motor cortex. With todays methods we can do an acceptable job at separating for example hand from foot movement. These methods look at the spatial domain, and do so in a way that is near perfect. And as you can see, there is a certain distance between the areas on the scalp, while the fingers are all in the same area.

So you couldn't distinguish individual fingers with todays technology. If it was ever to be done, I'd expect that it would be done with the same algorithms as we use today, but with much denser electrodes. If I were to bet, I'd bet that this would be physically impossible, but I'm not as confident as I am with saying we wont be able to detect who I want to call.

[1] http://en.wikipedia.org/wiki/File:Human_motor_cortex_topogra...