You can buy a PCMCIA card (PC card) complete with SIM card, that will fit onto a slot on your laptop and provide internet connectivity via the mobile phone GPRS General Packet Radio Service in most countries where GSM phone service is available.
This system works fine and requires minimum setup, but you are paying for an additional mobile phone service even though you most likely already have a GSM mobile phone that you use for voice calls.
A more cost effective solution might be to get a GSM mobile phone that can connect to your laptop via a USB cable and, with some interface software, be used in exactly the same way. The advantage is that you can use the same phone and SIM card and service for voice calls and for internet access.
Howard [ Just Imagine ] 22-Mar-2008