Texting internationally is no different from texting within your country.
You just need to have the recipients number, go into your messaging app and send the message.
Be aware though that often, contacting numbers from different countries can carry additional costs.
Contact your phone service provider for more information on your rates and costs.
Another thing to keep an eye on is the use of area and country calling codes.
Hereis a list for US state area codes, andhereis a list for international country calling codes.
