At the CeBIT kick-off press conference today, T-Mobile Germany and Asus announced an interesting cooperation: T-Mobile will start selling the eeePC in Germany and Austria with access to their Wifi and 3G networks. The 3G offer will include an HSPA USB stick. I've just recently bought an eeePC myself and time will tell how often it will be preferred over taking a full notebook with me. But I think chances are fairly high since it nicely fits into a bag and weighs almost nothing compared to the notebook.
For those who prefer using their mobile phone as a 3G "modem" for the eeePC (like me) instead of being locked to a single operator, here's a link that explains how to do this as well. I tried with an N95, a Nokia 6680 and a Motorola V3xx and they all worked fine.