Skype is unique in that it offers more services and capabilities than any other messaging platform.
1. It makes video calls, even conference calls
2. It is an instant message/chat app
3. It is an audio communication app
4. It is a file transfer app
5. If can also be a full phone with voice mail (pennies per minute)
The bonus is it is ubiquitous and has a huge cross platform install base. I've used it and never had any issues at least with the desktop version. Sometimes the video stutters a bit but that could be caused by any number reasons unrelated to the app. It used to drop a lot of phone calls only on iOS but that got sorted out a few versions ago.
iMessage does literally all of this, minus the phone. If you have an iPhone, it does all of this.
I did not know that.
Really does iMessage make video calls?
Does iMessage make live audio calls?
Does iMessage make file transfers?
I knew it made audio messages that have to be downloaded but is it like Skype which is audio just like a phone, chatting in real time?
Also the cross platform aspect is a big factor for me. All of my siblings and my parents are Windows people. You know the deal, they work for the government or large multinationals and are entrenched in Windows, You can pick your friends. You can't pick your family. I use Skype to communicate with them regularly.
No it doesn't. And it only does some of this if the other person has an Apple device too.
iMessage + Facetime comes close, but still doesn't do conference video calls. And I don't think you can tranfer generic files. Photos, contact cards, and voicemails, ok, but not any old file.
And, as you mentioned, you need phone.app for voice calls to a non-Apple device.