Try out the popular Skype service to make video or audio calls to anyone in the world who has Skype on their phone or computer. You can also make calls to any regular phone number, whether or not there is an associated Skype account, for a small fee.  Download Skype for free on a smartphone, tablet, or computer to immediately begin calling other Skype accounts for free. If you want to use Skype to call a regular U.S. phone number, add Skype Credit to your account to pay as you go, or select a monthly subscription to save on frequent calls.  Make sure you are connected to a computer or phone with high-speed internet when you make calls from Skype, as the audio and video quality will be better and more reliable with a good connection. Note that if you use a mobile app for Skype on a phone or tablet that is not connected to WiFi, you will incur data charges. Check with your phone or SIM card provider on these charges, or purchase a plan with unlimited or a large amount of data if you plan to use phone apps frequently without an internet connection. Use another service with audio and/or video calls available, such as Google Hangouts, Viber, or WhatsApp. Like Skype, calls through these services are free to any other members of the service and have a small fee for calling regular landlines and cell phones.  Use these services on a computer or through free apps for your mobile phone or tablet. Remember that if your phone is not connected to the internet, you will incur data charges for the calls you make on the network. Try out different services to see which one you like the best, as they all have slightly different features. Or, you might choose an app based on whether your U.S. contacts also have it or can get it, because then your calls to them are free. Load contacts, phone numbers, or credit (if applicable) for calls on an internet phone service or app before you use it to call the U.S. from the UK. Familiarize yourself with the process of making a call, the quality of the audio or video, and any other...

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Write a summary of the previous text in Vietnamese:
Dùng Skype để gọi thoại hoặc video. Thử những ứng dụng gọi khác. Kiểm tra dịch vụ trước khi sử dụng.