One solution is (and this depends whether in your country telemarketers target private or business numbers) to tell the callers you're not a private (or a business) number, whichever they're not interested in, but a corporate and make the impression that it's never appropriate to call you now or ever again. Telemarketers are interested in people who can listen to their talks (automated or in-person) so if it's not possible, they will cross you off the list soon.
Another way is to set your phone in fax machine mode (real or faked) while you're not expecting any calls. Surely, cold callers have systems in place to quickly stop trying on numbers that appear to be impossible to get people on.