I got brand new 4s Iphone white from T-MObile. I am from MAcedonia. And just right away i face this issue.about 1 in 10 calls I get no outbound audio when dialing. Call shows the timer counting as if the call is progressing but absolutely no ring back and cannot hear the party on the other end when they answer. This is fixed if i press speaker button twice. And the second problem of 4s i s that somethimes 20% of it , i can hear the other side , but they cant hear me, so i have to do it again the speaker button twice to fix the problem . I am very frustrated. Here we dont have Apple store , so i am in trouble. In Monday i am going to T-Mobile , to ask for a new one replacement. Shame for apple ,for prettending that aren't
aware of this issue.
Does anyone here is faceing this problem too?

I can only claim experience with the US AT&T locked version of the iPhone 4S, but my wife has not had any of the issues you described... She was hit by the battery issue but 5.0.1 fixed that for her... Hopefully T-mobile will switch the phone out for you!

Take a peek here:

http://www.hackint0sh.org/f143/333652.htm