sounds strange, maybe a restore in itunes would fix that.
What I have found out is that the VC works best when you use "call" for names and "dial" for numbers. don't ask me why, but for me this way it works best. for some reason, when I try to call a number with "call" it often starts with a 1 I didn't actually say.
but what does your phone do when you try to dial a number? does it also say "no match found" because that really shouldn't happen (when your number is long enough! "dial one" might be seen as a name because it's so short)