I see two main ways to monetize it. If it's calling you or texting you, you should be able to text an advertisement or leave a voicemail as an advertisement.

I see two main ways to monetize it. If it's calling you or texting you, you should be able to text an advertisement or leave a voicemail as an advertisement. I'd also consider telling jokes or something that gets people to spread the service and make it viral. Randomly mixing jokes and ads might not be such a bad bet. The other option is impressions on the website. Either of these probably won't result in much money, but it should pay for part of the service.