A very promising decision by a federal appellate court has closed the door on robocalls to cell phones.  Interpreting the Telephone Consumer Protection Act (TCPA)  broadly, the U.S. Court of Appeals for the Third Circuit ruled in Gager v. Dell that, under federal law, a consumer can revoke prior permission for a company to call a cell phone number.    The court relied upon the TCPA and an FCC ruling that gives customers the ability to revoke any prior consent for a company to call a cell phone number.
If you receive robocalls (automated messages) from any company with which you have done business in the past, you need only write a letter to that company specifically rescinding their right to call your cell phone number using any automated dialing service.    You might even want to mention the decision in Gager v. Dell just to make sure they know that you mean business.