I think all of these tools can be useful. Depends on the person and the situation.
During a workday, I won't respond to anything non-work related except for text or emails (and don't expect a quick response). But on the weekend, I love long phone conversations. FB and twitter are good for keeping up with casual acquaintances, and for getting news across to lots of people quickly and easily. For my best friends, nothing beats face to face. I haven't used Skype much, but I'm sure it has its use, too.
I'm the opposite of "always available". I'm available when - and only when - it suits me. I know a lot of folks will consider that selfish; I consider it practical. Nobody actually multitasks well and I like to give my full attention to whatever it is I'm doing. The upside for my friends is that they never have to deal with the annoyance of me checking my text or emails when I'm with them. I shut off my phone whenever I'm with someone I care about. I only wish I was better about remembering to switch it back ON!