Cellphones have a regular connection to a cellphone tower that lets you dial numbers and talk. I’ll call this the voice channel. Smart phones also have a data channel where you subscribe to a data plan that is managed and billed by the cellphone provider. It uses the same cellphone towers as the voice service.
A cellphone may also be able to connect to a WiFi (wireless Internet connection) which is not managed or owned by the cellphone provider. This wifi may be your own wireless router at home or one at a hotel, coffee shop or supermarket. The wireless connection may also be someone’s personal router that they have not secured.
By turning off your cellphone data channel and using wifi when in range, could substantially reduce your data usage through your cellphone company. I do this at home especially since why use cellphone data capacity when mine at home is unlimited usage and right there.This can be compared to the old idea of making calls at home because they may be free rather than use a payphone when traveling.
So if you are traveling, you may find that you want to disable the phone (voice and data) services on your smartphone and just use a wifi connection on your smartphone. There are applications that allow you to connect to VOIP services through a wifi connection, thus, you could go outside a coffeeshop in London and perhaps pay a penny a minute to call the U.S. or just use Skype or another service to make free calls. You should test these things before starting your trip, then just look for wifi in the remote location. With wifi, you will not be able to use your cellphone while driving, for example, and you may have issues finding a free wifi connection and have to pay for one (like at some resorts). Still, you may be able to use your current smartphone for telephone calls, Internet browsing or to watch TV, while traveling without paying roaming charges, etc.
Alternatively, you may be able to use the data channel with a cellphone app to make calls overseas that would normally be carried by your cellphone provider at a greatly increased cost.