It'll be a PCMCIA data card. Most of them are specifically branded by the mobile phone carrier and may have a SIM card slot (if it's for GSM) and use GPRS/3G/EVDO or whatever your carrier supports. For example, if your carrier is GSM and only has GPRS (which was the norm here until a few years ago), then they're normally called a GPRS PCMCIA data card.
That will get you online wherever you have a cell signal, for varying cost.