I'm not a lawyer, but I don't see how they could legally restrict you from joining a class action lawsuit, even if you sign a contract saying so; my (very) limited understanding of contracts leads me to believe that illegal contracts aren't enforceable in court (i.e. AT&T couldn't enforce a service contract that says you have to shoot your neighbor if you terminate the contract before 2 years, because that would be forcing you to commit an illegal act to satisfy the contract).
I'm not sure whether this clause would stand up in court, especially if AT&T were discovered to be doing something skeevy that only a class-action lawsuit would provide effective relief for. However, in general, a lot of consumer contracts have mandatory arbitration clauses buried in the fine print and the courts have been happy to delegate their work to the arbitrators.
Also remember that companies are happy to put all sorts of unenforceable terms into their legal boilerplate, to intimidate customers who don't know better.
If I were writing the laws I would enact a very strong presumption against mandatory-arbitration clauses in any contract of adhesion. But I'm not.
I agree that it's unlikely to be legally enforceable, I'm also pretty sure some states are moving to make portions of contracts requiring consumers to waive certain rights invalid. (Your example of being required to shoot a neighbor is clearly nonsense however).
Until it's tested in court though we'll likely never know. I assume part of AT&T's rationale is that:
A) They have the time & resources to argue then appeal this point for many years should any significant class action arise.
B) It may be enough to discourage consumers from joining aclass action. In many class actions the only people to see significant money are the lawyers. Consumers usually receive something of nominal value and if AT&T were to highlight this cause it may be enough to persuade most people not to bother.
Sorry, I knew that was a nonsensical example, I was just trying to make a clear example that they couldn't put any language into the contract that you couldn't legally fulfill.
In any case, I fear that you're very correct on both points. Even if it's not legally enforceable, it's going to cost the average consumer more than they're worth to fight it and have it nullified.
By federal law, they cannot prevent consumers from joining class actions. However, they can in some states.
Also, there's a difference between an illegal contract (which is a nullity and for which no remedies are available in case of a breach) and an unenforceable contract (which may still be enforceable under theories of unjust enrichment, promissory estoppel, etc). A contract to do something illegal is an illegal contract. A contract with unconscionable (per se unfair) terms is usually an unenforceable contract.
