Ask YC: What do you do about spam?

Hi all. We're a small team (5 people) but are inundated by spam. We've all got iPhones or Blackberrys and so have been looking for online solutions which will filter the spam out before the email hits our server. We tried one company, but they're wanting to charge us over $2000/year for this as a service and I was wondering what you do about spam? Are there any low cost (but good) services that you would recommend similar to the above?

Thanks!