I can take my unlocked GSM/3G phone to a foreign country, buy a local prepaid SIM card for less than €5, and save a fortune on roaming charges. Operator competitiveness is enhanced when I'm not abroad, since they know I can dump them any time - so long as I didn't take a 'free' phone with a long contract - and go with their competitor. I pay €9 a month in Finland for a phone line, no included minutes/sms, and uncapped 384kbps data usage, on a rolling one month contract.