I love Skype. I can send texts to mobiles and my own mobile phone number shows up - a real boon as I hate texting on a mobile and it so much easier on my keyboard.
I do not have a land line at all and can make and receive cheap / free phone calls to land lines anywhere in the world. Free calls to people who also have Skype.
I use Skype to IM all my friends as I hate MSN with a passion.
I have a Skype phone, connected to my router, so it works whether my pc is switched on or not.
I can conference IM, so lots of us can IM together. I have webcam so I can see my friends.
Skype does it for me.