National Geographic and Playa del Rey, California-based Cellular Abroad have partnered up to deliver a pre-paid worldwide mobile phone. The quad-band "Talk Abroad Travel Phone" will work in over 100 countries and users will get to keep the same phone number, no matter where they go.

Since the phone is pre-paid, there will be no monthly bills or contracts to sign. Users can purchase the phone outright for $200 or rent it for around $50 a week. The phone includes a SIM card that has 30 minutes of free outgoing talk time. Additional SIM cards will be $80. In many of the countries, all incoming calls will be free.

Tech-savvy phone dealers have been selling unlocked phones for years. Unlocked phones will generally work in another cellular phone network as long as you buy a new SIM card. This practice is big in Asia where the phone companies make most of their money by selling talk-time refill cards. In the United States, phones, which are cheap or even free with a monthly contract, are locked to their respective carriers and often will not work with other carriers, even if you put an international SIM card inside.

The phone package will also include international charging adapters and access to a toll-free number for travel help.