Problem with iPhone 4

ust got the iPhone 4 a couple of month back and I keep having problems with it. Just wondering if any fellow iPhone owners here could tell me if this is normal or if I should go to the Apple store for a replacement.

Basically, there are 2 problems. The first is about 50% of outgoing calls fail and I have to keep retrying before it finally goes through. I have also been experiencing really bad signal during some phone calls, even when outside. The second problem is when receiving phone calls, the 'Slide to Unlock' doesn't always work and as a result I keep missing important calls. The minute the call is missed, the phone unlocks just fine.

Obviously these 2 problems are getting increasingly frustrating. Is this a problem with my phone? Or just a problem with Apple's bad design? Because it's not worth going in to the store just to get another phone with the same issue. Especially since they will probably tell me it's 'water damaged' like they did with my 3GS just to get out of replacing it for free.