As we just noted earlier today, iTunes is feeling the hurt of all the traffic today. Case in point: Activation is confirmed to be down all across Canada. We're also getting reports that some people who did manage to buy an iPhone 3G are stuck in emergency call mode and can't activate. It seems that activation is so tough right now some AT&T stores are letting customers leave without activating their iPhones. Our advice: do not leave the store without getting it activated, at least for today.
Meanwhile, there's even worse news: people who applied the 2.0 update to their first-generation iPhones are reporting in the comments that since iTunes is hurting so much, they can't connect to activate their phone.
In other words, hold off on that update for a bit, otherwise the only person you may be able to call today is going to be 911, and as unhappy as you may be about the entire situation, the police really don't want to hear about it.
Quick Update: If you're looking at a non-functional iPhone 3G that can't be activated but your old phone had its SIM de-activated, pop the new sim out and slap it in your old phone so you can at least make some calls and suchlike.