Sorry to hijack your thread but I have the same problems. The only person who I feel totally at ease with, and can always make conversation with is my long-term boyfriend. Even with my small group of best friends, after a while I'll find it hard to think of anything to say. I'm just not chatty at all and I worry that people will mistake this lack of things to say for me being a really boring person. I pretty much avoid talking to strangers and if someone new tries to introduce themselves at a party I just politely say hello then find and excuse to get away before they try and start a conversation.
I'm absolutely terrible with phones. I don't mind answering my mobile because I know who's ringing, but if I'm at home and the house phone rings, I hate answering and generally don't, which annoys my mum, but I really do fear answering it!
It's so bad that in my student home, if I know that one of my house mates is leaving to walk to uni at the same time as me, I'll go ten minutes earlier to avoid walking with them, and thus avoid awkward conversation. But if there's more than one person walking to uni, I'm happy to walk with them. If I do find myself stuck talking with a person I don't know that well, I always revert to small talk, and as a typical Brit, I usually end up commenting on the weather.
I think it's partly the reason why I've put off getting a job for so long. I had one for a couple of months when I was 16 but my boss was shouty and strict and I could never follow her instructions. I'd also find it really hard to work in a shop or restaurant because if I saw someone I knew or had to serve them, I'd feel so nervous and embarrassed. I definitely wasn't this bad in my younger teens, but now I'm 20 and I feel so socially retarded!
Sorry that I can't offer any help OP, but at least you know you're not the only one.