IPhone 4 not receiving calls?

For about a week now I've noticed that my iPhone 4 (which I've had over a year) has randomly not been receiving calls when someone has tried to contact me. It's become quite a problem because my doctor will try to call me and my phone won't say someone is trying to call. I don't have insurance on this phone though! So if there's something actually messed up on it I'm screwed. Will iOS 6 fix this? I never downloaded it because I don't have enough space on my phone with my pictures and music (6.4 gb) but I deleted my music because I really need this problem fixed. Will iOS 6 fix it? If not what else can I do?

If you don't have insurance then if your iPhone is actually broken, even if it was broken since you got it and even if you have no warranty and no insurance, then your screwed buddy. You might have just wasted £600.