GSM and Sim Cards

GSM phones work on more telephone systems around the world than any other phone. If you're travelling from country to country, look into purchasing different prepaid SIM cards. SIM cards change your telephone number, but they also allow you to take advantage of in-country calling rates. The card usually comes with credit equal to the amount you paid, i.e. a SIM card costs 20 bucks and comes with 20 bucks worth of calling credit.