the only exception is if you have provided specific permission (and the caller must maintain proof) for them to call you and they can only call you for the reason you gave permission for.

Same is true for any solicitation call, no matter how it is dialed, to a cell phone. There are no exceptions, not even politicians. The DNC legislation exempts politicians from the DNC restrictions to landlines only. However, pols are not afraid to call cell phones because it is enforced by state attorneys general, who aren't going to go after other pols (the center that makes the calls would be fined, but not the campaign).

The reason you get so many robocalls is because there is no realistic way to track down who is doing it and if you do, the countries they do it from aren't going to prosecute. So, don't answer unknown calls, that is your only real answer.