If I make the call, I make sure I write down what definitely needs to be said on a piece of paper. Then I go to someone where I can be alone and make the call. Often I chicken out of saying everything on the list, which means that I'll have to make yet another call to make sure I ask next time (if its very very important, like an interview).
If I'm calling a friend we usually just say what needs to be said and the goodbyes are vey quick and easy, but saying ummm and errr whilst you think of something to say is pretty normal, even people who are great talkers do it a lot - complete silence is quite daunting!
And if someone calls me - I crap myself. :lol: