Most mods out there which tell you how to get internal 3G functionality are quite complicated and certainly not for the novice modder. João from BassoPT’s Ultra Mobile Computing has come up with a relatively easier solution that will only work on the Samsung NC10. However, this still involves opening the bottom of the netbook, so you’ll have to see where your skills fit before trying this at home.
João basically opened the bottom and replaced the Wi-Fi Mini PCI-E card with a 3G modem. Obviously this means that you’ll have no wireless access, but João solved this problem by using a small Buffalo USB 2.0 Wi-Fi dongle. The other issue is that once you insert your sim card into the slot it will remain there unless you take off the whole bottom casing again. Or, you could always hack a hole into the casing to provide easy access. JKKMobile says that this is one of the few netbooks where you swap out the Wi-Fi module for a 3G one.