In phone talk, roaming is what your mobile does when it is away from its usual network — often in another country — and has to connect to a different company's network so you can still call, text, or use data. That extra use is billed as roaming charges, which can be painfully high, so people buy a local SIM or switch data off. There is also roaming inside one country, when your own company has no signal and another network carries you. Though actually, the older verb roam still means to wander about with no fixed path; this phone sense is a later picture of the phone wandering onto someone else's network. Shops and phone plans in Taiwan almost always use the Chinese term, not the English word.