If there's truly a congestion problem, all users would lose speed. Which of course is exactly what happens. We've all had slowdowns at certain times.

The voice network has intermittent congestion. Today was an example. I had three dropped calls in my home. People are calling and wishing their friends and family happy new year, I suppose. It doesn't matter whether I'm within my plan minutes or over (and paying a premium).  If the network can't bear the traffic, my calls drop.  I'd love to see them send a text saying I've used too many voice minutes and now my call quality is going to drop. They won't shut off my service, but it wiil be harder to hear. 

There are times when more people are using data and I can't get pages to load. Then it eases up. Heavy users aren't doing any more to exacerbate the problem. It's the number of users at one time. Those on limited plans who are paying for overages experience the same slowdowns.  (I might add they can technically be charged $10 for one bit over 2GB. Nice racket there. With texting, you pay per text over. You're not charged for 1000 more. )

I don't see AT&T turning away any new subscribers because they can't handle the traffic. They are actually giving away 3G smartphones to sign up as many data users as possible. That will put a greater strain on the network.

Until they refuse to sell more data to people on tethering plans or tiered plans, I'm not buying that there's anything here but an attempt to pile on charges. As VZW and BofA found, consumers are getting to the end of their tolerance. Companies that have ongoing relationships with customers need to learn to create a sense of value for cost. I have to point to Apple, which does not nickel and dime their customers. People fall over each other happily trying to give Apple money and they don't begrudge it. Apple is highly profitable, rarely aiming for short-term gains. (The worst thing they did was a "priority" service program, which I think've now dropped.) They want people to keep buying more goods and services and talk about their positive experience. If the suits at AT&T (and others) would stop treating customers like cows to be milked, they might be pleasantly surprised. 

I agree with the above posts. I was going to give in and change to the $25 plan, but since there's truly no way to verify my usage, I'm skeptical of AT&T's billing.  I'd rather pay the extra $5/month not to get any big surprises.  In four years as an unlimited iPhone user, I've never used more than 2GB, but I'm afraid I would suddenly find I'm in that territory with no recourse except to move to Sprint  when my contract is up (and I'd truly rather not).