Further to my last post on lobbying, as mentioned, if you follow those steps (or any others that involve promoting your application next to the EC Units), that shall grant you some phone interviews. In my case, I had 3 interviews for 3 Units in 3 different DGs. For the first two, the procedure was the same: I received a call from an unknown number (please note that all calls from the EC will come from unknown numbers, so try to have your phone always next to you during that phase in order not to miss a call) made by the assistant of the Head of Unit, asking me if they could shcedule me a call with the Head of Unit for a suggested date and time. In both cases they suggested it for the day after in the afternoon.
Before answering the call, be sure to go to a place where there is not too much noise and where you can concentrate on the call, as, if you lobbied to several Units, you have to make sure you understand the first words from the assistant, which will be to identify the Head of Unit on behalf of whom they are calling. If you don't understand it at first (as you may be a bit nervous to know you're answering a call from the EC and sometimes it's difficult to understand the name of a foreign person, told by another foreign person - and all the mix of accents that arise from it), ask them to please repeat it (it's better that you do it rather than not knowing who will be interviewing you on the following day). In both my cases they also mentioned the name of the Unit, so that is easier to understand than a name (and when you have the name of the Unit, you can easily search again the name of its Head). In the third interview I had, however, I received the call directly from two members of the Unit which were calling me on behalf of its Head and the interview started right away.
Before answering the call, be sure to go to a place where there is not too much noise and where you can concentrate on the call, as, if you lobbied to several Units, you have to make sure you understand the first words from the assistant, which will be to identify the Head of Unit on behalf of whom they are calling. If you don't understand it at first (as you may be a bit nervous to know you're answering a call from the EC and sometimes it's difficult to understand the name of a foreign person, told by another foreign person - and all the mix of accents that arise from it), ask them to please repeat it (it's better that you do it rather than not knowing who will be interviewing you on the following day). In both my cases they also mentioned the name of the Unit, so that is easier to understand than a name (and when you have the name of the Unit, you can easily search again the name of its Head). In the third interview I had, however, I received the call directly from two members of the Unit which were calling me on behalf of its Head and the interview started right away.
As for the interviews themselves, they all started with saying that they had received my CV and indeed thought it fitted the work done in that Unit, then they passed on to general questions about myself (what type of work I had been performing in my current job) and then some specific questions about the Unit (why I had applied to that particular Unit, if I had knowledge of the legislation related to that Unit, if I had worked in issues related to the work that Unit performs, if I was interested in working in this work they were developing at the moment - and then they explained me the work they would need the trainee to do). In one of the interviews they also asked me how was my French level and asked me some questions in French. They all finished saying I was on the selected list for that Unit, but that the interview was non-binding and that I had to wait for an official confirmation from the Traineeship Office.
So, while it is a good sign to have interviews, they don't mean you are selected yet and you have to wait for the end of the selection process and for that e-mail from the Traineeship Office which will say if you were selected and, if so, to which Unit you were assigned. However, as mentioned, if you are not called for any interview, do not despair and start thinking you're not going to be chosen: there are many Units that don't do interviews or reply to the lobbying e-mails, yet they read them and choose you without telling you anything about it. So you may even receive a great surprise in the end! The fourth Unit which selected me, informed me of that by response to my lobby e-mail, they didn't interview me.
Finaly, how to prepare for the interviews. From the moment that you choose the Units you want to lobby, it is assumed that for some reason your CV fits them and that you have some knowledge of the work there performed, so you shall be comfortable with answering some interview questions in case you are called without notice. But if they schedule you a date, you have more time to prepare: go to the webpage of the DG and try to find the sections related to the Unit which will interview you. Find about what they have been working on lately, the general resume of their activities, in case it is a law related unit, the legislation that enforms the work there performed, etc. Try to do a basic research on that Unit that allows you be prepared to cover most questions possibly asked in the interview. You can also print some of that information and have it in front of you during the interview, as they may ask you something you're not so sure about and that way you can look in the moment. And, most important of all, don't be nervous and do your best just being you! The Commission staff I met so far was really nice and friendly, so just be relaxed and answer their questions calmly and I'm sure you'll impress them the same way your CV did when you sent them the lobby e-mail.