I too suffer from this problem. While I have no problem doing voice chats over the computer, I have issues with answering or making calls on my phone unless it is my mum or my boyfriend (caller ID is so very useful to me). I too usually let the call go to voice mail if the caller is someone that is not recognized.
I'll never forget the day it took me almost three hours to convince myself to finally call for a pizza delivery, even with my boyfriend's help. 8O
Making notes before you make the call is a great start. Having someone there to be with you while you make the call (if possible) can also be helpful. At the very least, it's nice to know that other people are finding talking on the phone is as scary for them as it is for me. Makes you not feel so alone, hm?