If I want or need to contact someone, typically the first thing I check is my instant messenger. I use Trillian, which keeps me logged into every IM service I use regularly (AIM, MSN and Gtalk). I also log into Skype on it if I need to. If the person I want to talk to isn't online or available there, I check Steam. If they're not available there, I text them. If I don't have their number or something, I message them on Facebook.
Calling people is, for me, an absolute last resort.
This is entirely because, while I have way more minutes and texts on my phone contract than I will reasonably use in a month, I grew up with SMS and instant messaging as my primary form of communication. I know that, if I send a message to someone, they're not required to act upon it immediately and can respond when they're ready to. Phone calls don't afford that luxury. If someone phones you, you have to decide to answer or decline the phone call right there. If you miss the call, you have to contact the person later to find out why they were calling you, unless they left a voicemail (and who does that?).
So when I want to phone someone, I have to take into consideration how busy that person is and how likely it is that they'll be available to both answer the phone and have a chat. I'm not sure if this is simply a problem I have or something, but I generally have no idea what time is a good time to call someone (which is why, in the years that she's been living away from home, I've barely called my sister even once.) I rarely even call my best friend for this reason.
This isn't to say I think phone calls are bad. Not at all, I'll defend the importance of phone calls to the ends of the earth. I simply think they could be improved. Skype (and other internet-based voice calling systems) give you a good indicator, by whether or not the person: A) is online, and B) has their status set to "Available".
Yes, I know I haven't posted anything in quite a while. I have quite a few draft posts, and for the most part I just can't be bothered finishing them. I will eventually, don't worry. I also have a lot more stuff I want to talk about.