Network,wifi and software

For some reason my iphone 4 searches for signal every now an then most of the time it does it it will come up with no network I always repot it but it still had the same thing and even when I've got full signal and 3G a lot of people say at certain time when they ring me it does go through and it takes ages to connect to my known wifi also some software will open then close on its own for no reason