Definition - What does World Roaming mean?
A cellular service that allows users to use their cellphone even when abroad. World roaming capabilities vary from carrier to carrier and largely depends on the kind of mobile phone standard used. That is, users have better world roaming (a.k.a. international or global roaming) capabilities with a GSM-based cellular company compared with a CDMA-based one.
Techopedia explains World Roaming
In order for you to enjoy international roaming, your phone should be compatible with the kind of cellular networks present in the country you’ll be visiting. In this case, the best option is generally GSM. GSM is the standard all over Europe and it also dominates in other parts of the globe.
However, it doesn’t mean to say that if you have a GSM phone, you’ll automatically be ready for global roaming. Note that there are four GSM bands: 850, 900, 1800, and 1900 MHz. Now, not all of these bands are used in all areas. For example, Europe only employs the 900 MHz and 1800 MHz bands. On the other hand, only the 850 Mhz and 1900 MHz bands are used in the US.
What is needed is a phone with a tri-band feature, or, better yet, a quad-band phone. With a tri-band or quad-band phone, you can either avail of the international roaming services of your home carrier or have the phone unlocked. Once unlocked you can then simply purchase a SIM card at your destination. This will enable you to seamlessly access the local GSM network there.
Now, it also doesn’t mean that you cannot enjoy world roaming if your carrier runs on a CDMA network. There are large CDMA-based networks in the US, India, Japan and even China. Some cruise ships also support CDMA devices.