Sony-Ericsson just announced their new wireless HSPA Expresscards, EC400 and EC400g. Packed in the Expresscard/34 form factor is a mobile broadband modem that supports up to 7.2 Mbps downlink and 2.0 Mbps uplink on both the 850/1900/2100 Mhz HSPA/UMTS and 850/900/1800/1900 Mhz EDGE/GPRS bands. The EC400g has an additional GPS receiver.

With these cards, there is no reason for you to be disconnected - unless you cannot afford the card and/or the tariff. :) I wonder when they will release their USB version that will work with the macbook air.