How useful is cold calling?

[Joseph R.]

Hey guys - how useful is cold calling as a strategy to get new clients? My wife is trying to become a realtor - I drilled it into her head that cold calling is the key to success but after making about 500 calls shes had little to show for it....She's employing other marketing strategies but I'm wondering if I should tell her to give up cold calling for now or just blame the lack of activity on bad luck and carry on. What do you guys think?