Can you do a phone call or telconf through Skype or Google Plus when traveling on the ICE in Germany?

German ICEs have some coaches that are considered to be "quiet zones" and some coaches are "talking zone". There are symbols on the walls that tell you what zone you are in. The symbols can be seen here:

http://www.bahn.de/p/view/service/zug/handy_u_ruhebereiche.shtml

So technically having a telecon is allowed in the "talking zones". For fairness, it is commonly accepted that phone calls should be short, however (but there is no actual rule for this). For longer calls (on a cell phone), you can move to an area in the train without seats (e.g., next to the doors), where this will not disturb anyone. However, you will likely be disturbed there from time to time (e.g., when stopping in train stations).

However, internet connection will be the problem. The Wifi is not free of charge and often reported to be unreliable. It is also not available on some routes. The following map shows where pay-for Wifi is available:

http://www.bahn.de/p/view/mdb/bahnintern/services/mobilitaet_service/zug/wlan/mdb_113497_karte_railnet_ausbau_2013_vektor_apu.pdf

If you are traveling first class, it may already be free of charge - this change was recently announced.

Connectivity by phone is also typically bad and will only work with interruptions. Even regular phone conversations (which should work most reliably on a train among all forms of synchronous communication) are often interrupted during cell handover when the train is too fast. Depending on from where you travel to Berlin, the train speed can exceed 250 km/h - I am not aware of a carrier that offers a reliable connection then. Along many routes (even main ones), there are some parts in which there is no reception at all (as there is no base station nearby).

The other answers so far have been mostly from a social aspect, I want to add an engineer's aspect as well: most mobile phone technologies have a "speed limit" at which they can reliably work. I am not referring to data transfer speed, but to relative speed between the handset and the base station. Depending on the exact technology (GSM, GPRS, EDGE, UMTS, HSDPA, LTE), those limits are somewhere around a few hundred kph … well within the vicinity of the cruising speed of an ICE (up to 300 kph / 185 mph on a high-speed route). Which means that you will be operating on the limits of the technology.

Plus, you are sitting inside of a metal cage!

Also note that you will be passing through large areas with lousy cell reception. High-speed rail lines tend to stay away from people, after all, for safety and noise reasons, but carriers only build cell towers where there are people with cell phones. You can't expect 4G, maybe even 3G outside of major cities.

On every ICE train set, there are some cars which are equipped with cell repeaters, but a) they can only repeat a signal that is there (see previous point), and b) they are GSM repeaters (they might have upgraded them to UMTS, but certainly not LTE).

From personal experience, I can tell you, that I get a data connection only when stopped at a train station. (I usually sit in the "quiet" cars, however, which I suspect are not the ones equipped with repeaters.)

I haven't used the onboard WiFi, which uses the railway communication network to connect to the Internet, and is thus more reliable than cell service (but reportedly still spotty). But the railway communication network was never designed for high-speed data transfer. The bandwidth is rather limited and latencies are high.

Your best bet is probably gonna be an actual telconf (i.e. using just a normal GSM phonecall rather than relying on a stable data connection).

In addition to the info provided by DCTLib, do note that there is a bar (called “Bordbistro”) and in most cases a “restaurant” area where you can seat. If you do manage to set up a connection (and like others have already commented, I doubt that you could get a really good one), you could also look for a compartment (unlike Thalys or TGV, ICE trains also have a few compartments in each carriage) and with a bit of luck find yourself alone.

ICE trains also have something called a “multifunction compartment”, which was originally a family space (complete with toys) but can also be used for meetings. You will also need to be lucky to find it empty (there is only one per train!) but it's definitely a space intended to speak freely.