I usually use a unique email address for each corporation I do business with. For example, all e-mail from Ameritrade went to firstname.lastname@example.org. I notice that a few companies will give your email address to outside parties in violation of their privacy agreement. I am shaming them here.
From early 2006 (earlier?) to mid 2007, Ameritrade had repeated compromises of their list of email addresses. I received a lot of stock advice spam (fraudulent "insider tips") because of this. They refused to acknowledge the problem, sending out a ridiculous (and deceptive) form letter to users who complained about it. Then they would give your new address out. It was terrible. They recently declared the problem fixed, and maybe it is. But despite the sensitive security nature of their operation, they refused to address this problem for more than a year.
The address I've only used for interactions with Sprint customer support is now receiving spam from a housing market website of some sort.
Sprint deserves an entry here anyways just because they kept on calling me in the weekend mornings to tell me that for only $20/mo more I could have two phones. But that's another story.
Comcast's spamming of its customers is so inept that they were briefly famous for using a robodialing service that would deliver customers to a dead line. Nothing says "trust our info tech!" like using google to find out who called you to deliver a silent robocall. Around March 2011 I had a lengthy conversation with Comcast phone support, and he assured me I was on a do-not-call list within Comcast and would not receive any further robocalls from them. But dude was lying and today (December 2011) I received a phonecall from 877-842-6622 telling me to buy more Comcast services. I got on the phone and started yelling at the poor guy on the other end, when the light bulb went off over my head! I can win!!!
I told him that if he did not change my account number to 212-555-1234, I would cancel my service. He was only too happy to comply.
555 is reserved by the telcos for fictional numbers (such as for use on TV shows), and usually redirects to directory service (411). Booya!
(you could use Google Voice or something if you wanted to actually be able to have a real phone number with them)
If only I could lie to my telco about my phone number, I would be able to be a T-mobile customer again.