No sound on speaker/headphones when calling

Hi everybody,

I've got an iPhone 4S which doesn't make sound when calling, via headphones, via ear speaker of via speakerphone. I don't hear my calling partner...

When I play e.g. a Youtube video, I can hear sound via speakers, and also via headphones when I plug them in.

So, long story short, only when using the ' telephone' I don't get any sound whatsoever...

I replaced the ear speaker, restored iOS, nothing helps...

Edit: The microphone doesn't seem to work either, when calling. Siri does work...

It kinda works like an iPod now, instead of an iPhone...

Please help?