Depending on your carrier, they may have an International calling plan you can add for a small monthly fee. Here is a description of AT&T’s plan, for example—>https://www.att.com/shop/en/wireless/international/long-distance.html
Other options include:
- Skype: Skype to Skype is free, Skype to landline is about 2¢ a minute to Europe.
- FaceTime, but only to Apple devices (iPhone, iPad, Mac)
- Google Voice: Free for calls in the US, about 2¢ a minute to landline in Europe.
- Cable TV: Many cable TV providers offer VOIP phones that have very attractive rates to other countries.
With Google Voice you get your own free phone number that you choose and that you can receive calls on and call out from using the GV app.
You can also get a phone number with Skype, but it isn’t free. It is reasonable, however. And you can choose a number in other countries, so, for example, you could have a UK phone number that reaches you in the US.
There are also the messaging apps mentioned by Phil, but they only work between users who have the same app. WhatsApp, Google Duo, Google Hangouts, Telegram, Signal, Facebook Messenger, etc.