Dropped calls with grey screen

[mamaruth]

I am having trouble with calls wherein I can't hear anything, but my phone says I'm connected, and when I try to hang up, my screen goes grey. Sometimes I have to push my power button before it will hang up. Occasionally it will tell me I am in airplane mode. If the friend tries to call back immediately, it will sometimes go through or sometimes tell them I am not available. Any suggestions? It's getting embarrassing.