Please choose the correct ending to complete the given sentence: Computers and Electronics: [header] How to get free phone calls with smartphone apps [title] Notify your friends in advance that you're about to use an app to communicate with each other. [step] Tell them to download the app, which will be explained later in this article. [title] If your phone has a data limit, check if you still have at least 500 mb of internet data.

Ending1: [step] Knowing how many dollars you have is important. If you are willing to spend, it's worth it. Ending2: [step] Then, add it up and wait for someone to call. If you've 99 mb or more on your phone (if you would like to have a continuous internet internet connection), uncheck the limit. Ending3: [step] Add a cellular number to your data usage if you have one. [title] If your device reaches a minimum volume, your data usage will go up. Ending4: [step] You might want to use a free public wifi if you have no data (or have little data left). [title] On your phone, launch the respective app store.

Answer format: ending1/ending2/ending3/ending4