I suggest you check out the following blog post about Apple/AT&T requiring a social security number to activate the iPhone.

Read the comments as well, people are skewering the author for writing the article and calling him all sorts of names. And a ton of these comments are missing the point. The most poignant criticism is:

• All the cell phone carriers ask for your SSN in order to check your credit. So the title of the article is riding on the wave of iPhone news, but then again the issue arose because of the author's direct experience. So this specific example is just one of many inappropriate uses of a SSN for identification. The article therefore isn't particularly exposing a new issue, but it does give some interesting historical information and background.

Personally, I am amazed at the hostile response to the post. As mentioned in a few comments, places like Canada and the EU manage to have cell phones without giving away this kind of private information. I'm sure we could figure out how to do it here. But the main opinion of many of the posters is "of course we have to give our social security number over" because how else would the companies know who they could sell to? But why are all of these people on the side of business rather than wanting to protect their own interests? Where is this level of trust coming from? Why shouldn't we demand that corporations find another way to judge who is an appropriate risk?