I don't think common netbooks come with Sim card slot; it's a feature for the Tablets actually. For netbook you can get a USB Sim card Reader or DataCard reader to use it by plugging the Sim card in it and then connect it to the Netbook using USB port.
For netbook, only consider AMD Brazos based netbooks now and forget Atom. Brazos provides far better processing power and multimedia experience due to its more powerful Graphics solution (Radeon HD 6310M DirectX 11) and better processor performance.
Consider Acer Emaiche E644 around 17.5K.