From a UX perspective, it'd be great, unfortunately getting advertisers hooked into their system would need much more work than it took to actually build the project in the first place.

I was thinking of just putting it out for free until it got too expensive, then asking for donations and if that didn't make ends meet putting some restriction on such as advertisements or a time limit or something.

clearly your conference call gets rickrolled after 10 mins unless you call the premium no :P

Maybe the rickroll could start out quiet but just get louder and the other callers get quieter until you pay!