Here's an old gem of a trick for anyone feeling lonely, vindictive or very drunk: With Skype, you can connect any phones in the world and listen in on the results. Man, what a decade.
Here's the game, as articulated by Reddit user quicksilver 5:
Here's a fun trick - download Skype and set up a conference call by calling two of your friends simultaneously. They'll both answer and be thoroughly convinced that the other has called them. While you sit there at your computer trying to hold back laughter (or with your microphone muted), you can listen to them try and figure out what the hell is going on. If they chalk it up to an accidental speed-dial and hang up, keep calling them and hilarity will ensue.
Here's what you'll need to do:
1.) Get some SkypeOut credit: To call landlines or mobile phones with Skype, it costs money. You need to sign up for SkypeOut and buy $US10 of credit - the minimum amount available - which should supply you with hours of phone-to-phone pranking. I had some Skype credit sitting around already, because SkypeOut, in addition to offering local calls for a few cents a minute, offers international calls at extremely low rates.
2.) Choose your victims: Who, of all the people you know, would you like to call one another at an inopportune time? Because you can pick whoever you want. Arsehole boss and his terrible ex-wife, at 11.59 on New Year's Eve? Why not! Two people who you know will be in the same room at the time? Even better. You can add more than two people to a call, but two is the funniest, since it's not obvious there's a conference call going on.
3.) Organise the call: Under the "Call" menu in Skype, select "Start conference call". To add someone to the call they need to be in your contacts, so make sure you've added your victims to your main Skype list first.
4.) Do it: It may take a couple tries to get them to both pick up, but nobody's to alarmed by a phantom call or two - they happen all the time. After your first call, which your victims will have probably write off as a pocket dial or something, do it again. And again. And again, until things start to feel dangerous. If you can't keep quiet, hit the mic mute button in the Skype call window; you'll still be able to hear the other callers, but they won't be able to hear you.