I regard registered SIMs as disadvantageous, since that may have an impact on validity, you don't know who used it for whatever purpose before (e.g. cirminal usage or just disturbing calls for the previous owner) and as you stated it's problematic as soon as you need to authenticate to customer care for whatever reason.

@andy
Simyo is only available online. Their flatrate doesn't require a German bank account - you just need to have € 15 of credit in your account to activate the flatrate option.

Free Congstar cards
 

If you know someone in Germany, perhaps they would be happy to apply for a free Congstar card for you.

The offer is here: http://mp-success.com/mpa/wm/000350/?partner=cst_ppd

In Germany, you can buy or top up the card at many locations: gas stations, "real" supermarkets, "Extra" Supermarkets und "DM" drug stores, etc.

There is an excellent wiki with information about all the German prepaid cards:

http://www.prepaid-wiki.de/index.php5?title=Hauptseite

Thanks for that tip! Great offer. I have applied for one.

Which German network does a number belong to?
 

In Germany, people are allowed to move telephone numbers from one telephone network to another. But this is not a problem because it is easy to test which network a telephone number belongs to.

From T-Mobile network (and from T-Mobile discounters: Congstar, etc) dial: 4387
From Vodafone network (and from Vodafone discounters: smobile, etc) dial: 12313
From eplus network (and from eplus discounters: simyo, etc) dial: 10667

From O2 network (and from O2 discounters: Fonic, etc) send an SMS message to special service code 4636 with the text: "NETZ telephone number". Do not include the quotation marks. The SMS is free of charge.
Example: NETZ 01761234567

All of the above methods are free of charge, when they are internal network calls. These numbers can save a lot of money if you use a German flatrate tariff together with a second SIM.

I noticed the Flat options on Congstar. Can these be booked for one month and then removed again, or is this actually a separate product?

I think I have decided...
 

I think I have decided what to do. For now NOTHING. Either when we arrive or before (Ebay) buy a T-MO with NONSTOP and activate it for one month.

I think my biggest expense has been and will be my wife's long calls to friends & relatives, usually on landlines @ home. Last summer it seemed best solution was 8 cents per minute with SUNSIM. T-MO Nonstop may have been available then, but as I recall, they kept starting and stopping the offer. It was not clear at the time if they would suddenly withdraw the availability as they have don with so many of their prepaid plans. Seems that is now a permanent fixture of their prepaid plan. We'll be in Germany 2 of the 4 weeks and I bet that will be the bulk of the calls. So, instead of 100 minutes at 8 cents, 8 Euro, that call will cost 29 cents. Of course for calls to non D1 mobiles, the card is a bust. That's why we have the other.

I'll probably still need a recharge on UM+, Simyo and the SUNSIM. At least the SIMYO can be 10 Euros; the others are more.

I'm trying to find out how much a T-MO starter pack (straight T-MO, no "provider") costs retail at a T-MO store. I'm guessing 20 Euros, maybe more. They are going for less, brand new, on Ebay.de, even with shipping. I previously had 2 cards from Viktor Vox and they have their own customer service. I think I would prefer to deal DIRECTLY with T-MO.

Again, I would appreciate any thoughts.

I think I saw the CONGSTAR FLAT was going to be 69.95 Euros per month. That is more than I hope to be spending for the NEW prepaid; I have the other cards.

Stan

That's for all destinations. I was thinking of landlines only for €9.99, with callthrough for from half a cent a minute

New Congstar flatrates - from 18th March
 

Correction:

At the moment, flatrates can only be added to, or removed from the congstar "postpaid" sims. Without any additional flatrates, postpaid sims charge 19 cents per minute for calls to all networks. Prepaid sims charge 9 cents per minute for calls to all networks.

Flatrates can be cancelled provided notice of the intended cancellation is given at least two weeks before the end of the current monthly flatrate period. Otherwise, the flatrate automatically continues for another month, provided the sim has sufficient funds.

I think that the flatrates can be switched off via the internet, provided the necessary notice period is given. Perhaps someone with a congstar sim can confirm this.

From the 18th March, the T-Mobile, vodafone, O2 and eplus flatrates will each cost 14.99 EUR per month. (At the moment the T-Mobile and vodafone flatrates cost 19.99 EUR per month.)

Flatrate congstar-congstar is 4.99 EUR per month. The flatrate landline tariff (to all german landlines, not just Deutsche Telekom Festnet) costs 9.99 EUR per month.

I have not read anything about "callthrough for from half a cent a minute".

One of the Betamax operators (Dialnow) charges half a cent per minute to landlines in several countries! There are access numbers for many countries including a 0211 number in Germany. See: http://www.dialnow.com/en/accessnumbers.html. The funny thing is that calling other Netzwerke in Germany is excluded from the German flatrate tariffs and is normally charged at something like 15c/min. If you did it via such an option this might cost only 9c/min.

In some countries and on some postpaid tariffs you can nominate a favourite number with free calls! In these cases nominating such an access number can make a lot of sense!!