gundar: Before you do this, consider that the police and hospitals remove caller ID too, so in the event a family member is in trouble (or your bestie needs bail posted), you may miss a critical call. While you'd also be missing calls from the IRD, they always get their money anyway, so avoidance is not any long term solution.
Possibly the best approach is to take the call and if it's not relevant just say - "I don't have the time to take this call, I'm busy [piloting a plane|delivering a child|commiting and act of violence] please send me the details by email" and follow that with your secondary (spam) email address. If the caller is after a quick buck, they won't go to the trouble of writing an email.
The problem is that if you're right in the middle of doing something that you need to stay focussed on then even taking 30 seconds to pick up the phone is seriously disruptive. I work on the assumption that if an anonymous call is important then the caller will leave a voicemail message.