From my experience, anything that requires a phone number is pretty tough to convert. Not saying this couldn't be profitable, but might be kind of tough unless you have a really cool service, etc. Other thing to consider is the very limited scalability if you're only willing to pay for 6 leads per days. i know i want to be able to really maximize anything I'm driving leads to... you could easily spend $660 just testing and optimizing to get this right, so then you are waiting 60 days before you see your first profit... yikes!
Also, you might get more prospects if you post what general niche you're in...