Roaming lets you talk, text, and go online when you’re outside of your wireless provider’s coverage area. With roaming, your data can travel on the network of another provider to give you the wireless connectivity you want. How Roaming Works

You may find yourself roaming if you’re traveling throughout the country, overseas, or during emergencies. During the 2G and 3G eras, consumers would see roaming charges broken out on their cellphone bills. Today, many providers offer nationwide plans, which typically include roaming along with unlimited talk and text as part of their service.

Here’s a quick overview of how wireless providers make roaming possible:

Your wireless provider operates your “home network.” If you are somewhere not covered by your home network, your wireless device looks to communicate with other networks that do provide coverage.

When your mobile device connects with another wireless provider’s network, the visited network identifies your home country and your home network. If there is a roaming agreement between your wireless provider and this other network, you’ll be able to connect to the “visited network” and make calls, use apps, and send emails just as you normally would on your home network.

Different network technologies and mobile devices need to work together to enable a seamless roaming experience. How Roaming Works

Network technologies. Different wireless providers built their 2G and 3G wireless networks using different technologies—GSM vs. CDMA, for instance. Today’s 4G LTE and next-gen 5G networks are built using common technologies, but because of the competitive nature of the wireless industry, providers are adopting these technologies at different paces. With nearly 100 wireless providers in the U.S., technological differences like these between networks can impact the ability of providers to roam together.

Device compatibility. To successfully roam, your mobile device must be able to work on the network technologies and spectrum frequencies used by the visited wireless network. Most modern wireless devices are built to operate on several different network technologies and frequency bands, but every wireless device is different in terms of which spectrum bands and technologies can be used.

Global factors. Wireless providers around the world run their networks differently based on their spectrum and technology mixes. To connect to a wireless network while overseas, your wireless device must accommodate the technologies and spectrum bands in use in different countries, and your wireless provider must leverage a global roaming agreement, many of which are already in place. (via CTIA) How Roaming Works