We knew this was going to happen and it did. Nokia fixed the problems with the 5800 XpressMusic NAM version and the phone has recovered its 3G capabilities which were lost a few days ago. It seems that it was all a software problem which Nokia fixed:

Following the introduction of the Nokia 5800 XpressMusic in North America, some consumers reported difficulties connecting with the local 3G network. As customer satisfaction and product quality are a priority for Nokia, we took immediate action by temporarily suspending sales and moving quickly to identify the root cause and resolution.

We have concluded this was an isolated situation related to a configuration change in the North American variant. We have now adjusted the configuration and will resume sales shortly. Those few customers of the Nokia 5800 XpressMusic who experience a 3G signal issue are advised to contact Nokia Customer Care. Our sincere apologies for the inconvenience.

The 5800 will be wearing a new firmware which should work perfectly. Nokia 5800 NAM will be available for purchase soon. If you already own one then you need to call customer care or visit a Nokia store to fix your 3G connectivity.

via Engadget