Here's how we handle it in the Netherlands (with T-Mobile carrier) - I just found out today, a few hours ago!
You go to the T-Mobile shop where you bought the product from and they tell you that it is the first time they hear about this no audio in outgoing call issue as well as the echo issue (which is just another potential problem with the iPhone 4S. I don't know how common echo problem is, but maybe because it is less disturbing than no audio, its topic is less lengthy). They tell you that they can take it and send it to repairment (because there's 2 years of warranty), and if it turns out to be broken, the repairment service will send back a new one. They told me this can take up to a month. I thought this is unacceptable and asked for an alternative. They told me I can go to the Apple shops in Amsterdam because that's where it will be handled anyway. I thought "OK! I will try lé Apple shop! Lé me don't want to wait for 4 weeks! And from what I read I see that it is likely that the new phone that will be sent might come with the same problems anyway!"
So I went to this "Apple shop" (in Amsterdam. There are I guess 2 or 3). They told me the following:
1- They are not an Apple store (and indeed are only called "iCenter"), but simply a reseller. They cannot help. They have nothing to do with phones bought from T-mobile or Vodafone or whatever carrier. There is actually no Apple Store in the Netherlands. And their answer to the question "Then, where are these phones sent for repairment?" is "Uhm I dunno :/"
2- These problems are indeed very common in the Netherlands with iPhones. They do not know why T-mobile says they hear it for the first time.
3- People in T-Mobile are always bullshitting.
So, the Netherlands totally failed handling this issue, I guess as most other European countries. Customers are being screwed by carriers, and carriers are probably being screwed by Apple who doesn't try its best to provide the best possible service.
This will not be forgotten you know. I'll never buy an iPhone again. The worst thing you can do as a company is to cast great doubt in the customer's mind about the well-being of a newly manufactured product. And Apple did not only do this but also failed to handle it properly. They actually failed to acknowledge it in the very first place. They think that there's nothing wrong with iPhone 4s? Why are they silent? Why don't they at least say they are working on it? Are they stupid, yes stupid enough not to see that their silence only will do more damage to their company? Isn't it more than obvious when they are selling malfunctioning products?
In whatever country you are: Tell people not to buy this product. There are zillions of complaints about vital issues like no audio in outgoing calls, echo, static noise etc. At least wait for a software update or a statement from Apple before recommending anyone.. I do not know what else to say. And customers: Please raise your voices because it is the very you who is being screwed up very badly and in an ugly way. It is your, or your daddy's or whatever's hours of work and money.