First, it appears that the first run of 5800s off the assembly line were manufactured with faulty speakers. Nokia has confirmed that the first supplier of earpiece speakers for the 5800 failed to protect them properly and prevent the ingress of moisture. Over time, moisture that got into the earpiece assembly ruined the speaker. Nokia said in an official letter to Mobile-Review.com:
All the faulty earpieces have been replaced with units produced by a different manufacturer, both those used in production models and those in the warehouses. I shall emphasize that we haven't changed the model of the 5800 XpressMusic's earpiece, but rather changed our supplier. It's easy to prove since the new units look differently.
Starting in late January all authorized service centers have been receiving packages with the new earpieces and any users who made warranty claims after that time shouldn't experience the problem again.
It's worth noting that the Nokia 5800 XpressMusic is one of our company's top-priority products, therefore its sales have been monitored by our Research & Development (R&D) division from day one, and as soon as we found out about this defect an official representative of Nokia's R&D department visited Russia to study the issue on-site.
So, 5800s made from late January on are sure be safe from developing issues with the earpiece.
That brings us to the 5800 NAM (North American variant). The 5800 NAM went on sale at the Nokia flagship stores in New York City and Chicago last week.
In NYC, users complained of the 5800's inability to find AT&T's 3G network. In fact, Engadget ran out to buy one, and experienced the same issues.
The Nokia Blog attempted to buy one last week, but was unable to. They were told that the 5800 NAM was no longer for sale due to the 3G signal issue. Apparently, phones were able to get AT&T's GSM/EDGE network no problem, but finding its 3G HSDPA network is a different story. Since nabbing some of AT&T'S 3G goodness is what the 5800 NAM is all about, it didn't make much sense for Nokia to keep it on store shelves.
I called the Nokia store in NYC, which confirmed that the phone is temporarily no longer for sale. Nokia hasn't responded officially, however, to the 5800's 3G signal issue.
So, buyer beware. If you're looking for a 5800, make sure it was manufactured after late January, and has a solid 3G signal before leaving whatever store from which you buy it.