Garry, a number religous groups tried this approach earlier this year when they tried to get Ofcom to ban Jerry Springer the Opera. Ofcom received around 20,000 complaints mostly standard letters. From what I read they all received standard responses back.
Well, it may have been 20,000 standard replies, but thats 20,000 pieces of A4 paper, 20,000 envelopes, all going through the franking machine at 21p each (I assume it's sent 2nd class!!), someone or more than one person to administer the address creation software.
All you need to do, is ask for a reply in the post, rather than e-mail, from some of these big companies. Each complaint costs them money to deal with, even if it's a standard letter. They will soon realise that dealing with complaints about costs of their 0870 number, is more hassle than it's worth.
We have already seen evidence in this site already. People working for companies have come on, and registered here, and voiced their own opinions, and even accused us of either being a bunch of whingers, ringing the wrong grographic number, and taking up too much of their company time dealing with these complaints.
Also, don't forget all those FOI requests that people have posted in this site. Each of these have required someone to personally deal with the issue and e-mail/post a reply for each request.