Motorola Milestone GSM :: Direct Settings To Bar Unwanted Calls?

I want to prevent advertisement calls and some calls from specific numbers in my Milestone 2.1 Update1. I cannot find any options for this in the settings menu of this phone. Hence at present I am saving these numbers to contacts and assign them silent ringtone. But the advertisers use to call from other unassigned numbers. I feel this much awkward and not the apt way. Other phones have a direct settings to bar unwanted calls.