Bat-basic telephony gear
Probably the easiest and most affordable piece of equipment that enables VOIP communication is the computer audio headset and any one of the many free PC apps listed in the Batphone Software section of this site. Headsets come in many sizes, shapes, and connector types. Most PCs come with at least two 3.5mm audio jacks, one for speakers or headphones and one for a microphone. Some PCs are also equipped with a third line in port. Basic PC headsets have two 3.5mm plugs: one for audio and one for the mic, while headsets for use with mobile phones have a single 2.5mm or 3.5mm plug.
More sophisticated headsets can feature USB connectors that let your headset serve as a separate audio channel.
This is handy for separating speakers that might play audio for music or game sounds from headphones that might play audio for voice chat or VOIP calls. Bluetooth headsets, commonly used with mobile phones, can also be used with a computer that has Bluetooth radio capability. In my experience, Bluetooth isn't as reliable as copper wire, but it can be more convenient. Most PC laptops have built in speakers, and many also have built in microphones, especially models with built in web cameras, so if you are just getting started with VOIP, you may not need a headset at all. Some models of laptop, especially thin models like MacBooks have a single headset jack for both audio and mic and require a mobile phone headset.
I have a folding headset that I keep with my laptop, and I keep a set of stereo ear buds with my smartphone, but for my desktop I have a decent pair of stereo headphones, so I use a standalone desktop style boom microphone.
I recommend using headphones and a mic, or a headset instead of speakers and a mic because some VOIP apps aren't great at filtering out background noise. It can be pretty annoying to hear your voice echo back to you on a one second delay, so do your friends a favor and use headphones.
If you keep your desktop PC on the floor, I recommend using the jacks at the back of the PC rather than plugging your headset into the front. Plugging into the front can be very convenient if you are plugging your headset in temporarily, but if you leave it plugged in to the front indefinitely it is likely to be damaged. I have had a couple of headsets stop working after rolling the wheels of my office chair over the cord several times. I have also stepped on a USB audio adapter accidentally and damaged it. If you plan on using a PC and a headset long term, I highly recommend using the rear panel jacks and threading your wires up the back side of your desk. It's a pain to do in the beginning, but it virtually guarantees that your headset or your audio jacks won't get broken. If you plan on alternating between headphones and speakers, I recommend a Y-adapter or splitter that lets you plug your headphones and speakers into the same jack. You can turn your speakers off when you aren't using them.