i feel your pain. :D
one of the few useful tips i picked up from conventional business books is that, before making a phone call, it really helps to write down a script for the call. obviously, you don't want to sound like you're reading it, but i know i've panicked when trying to ask to speak to someone, just not finding the right words, and having the words in front of me really, really helps. once things either go well or go badly, it's easier to just get on with it, but the other bits derail me pretty easily.
(and when i say script, i mean down to the 'hello'! for the factual bits, bullet points seem to be enough.)
best of luck with it!