what cellphone is best used in Germany/Czechoslovakia?, traveling from the USA?

First of all since 1993 there is no more Czechoslovakia anymore
It is 2 separate Countries Czech republic and Slovakia .

If you mean a provider for all 3 countries I would use vodafone.
Out of personal experience.
If it is for longer stays it might be usefull to change the sim card in each country.The EU has set limits to the 'roaming charges' that is to use a non national provider but it is still expensive.
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I live near the border to the Czech republic, and I'm using a prepaid SIM from Vodafone Germany for both countries. Mind that your cellphone must support the European GSM 900/1800 standards, so it must be a quadband. U.S. single or dual bands won't work here, tribands will have restrictions.

If your cellphone doesn't have a SIM lock, I'd recommend you buy a Vodafone prepaid SIM in Germany (branded as "D2 CallYa"). It goes for around 15 or 19 euros, with 10 euros credit for calls included, and you can easily top up on your credit at most supermarkets. (If you want to know how much money there is in your balance, type *100# and click "call".)

Of course you could buy two different SIMs, one in Germany and one in the Czech Republic, to avoid the roaming fees, but I don't know which Czech company is best.

Remember to buy a U.S./European voltage adaptor at home! You'll need to charge the batteries now and then, and there's 240 volts here.

For the best signal i suggest you to use Vodafone. The other prepaid cards are probably cheaper but Vodafone has the best signal and its so rare that you can not find a signal with Vodafone. Vodafone's prepaid card is called CallYa. you can buy it very cheap from www.ebay.de

last summer i had a blackberry pearl that worked just fine in germany, but i have cingular and the bill was very expensive

First, as already written, you need a cell phone that supports the GSM 900/1800 standard.

Second, it depends on how you're going to use your phone, i.e. only send SMS, place calls within Germany, place calls home and/or receive calls from home.

International calls are quite expensive, generally speaking I wouldn't use a cell phone for calls abroad. SMS on the other hand always cost sort of the same, no matter where they go.

There are four network operators in Germany, T-Mobile, Vodafone, e-plus and O2, the first two being the largest with _no_ difference in coverage today, almost 100%. Both T-Mobile and Vodafone operate in the Czech Republic and Slovakia, too, T-Mobile also in the US (not sure about Vodafone).

That said, it'd be obviously most convenient if you're already customer of T-Mobile in the US. Except for calling customer support once in order to check if the (free) "WorldClass roaming" option is already activated in your plan, you wouldn't have to do anything.
Just take your phone to Europe and you can be reached by the same number you have in the US, no matter where you are. There's also no hassle with European phone cards, everything will be charged to your account at home.

The same should go for many other US companies. You should definitly contact customer support and ask if a) your phone works in Germany, the Czech Republic and Slovakia and b) how much calls from/to these countries cost.
If your current cell phone is not GSM capable, you might be able to rent a phone from your phone company for the time of your stay.

More on using your current US plan below.

If you'd like to (or have to) get a prepaid card in Europe, then you will need to get separate ones for Germany, the Czech Republic and Slovakia, since the rates for using a prepaid card from country A in country B, calling country C are ridiculous - and it's not even sure that it works.

In Germany, it doesn't matter which company you choose, they all have more or less the same rates and offer mostly the same coverage (only O2 has a serious number of white spots), however T-Mobile has the most shops. Sorry if this looks like a T-Mobile commercial, but T-Mobile is the former state-owned German telephone company, that's why the pink T logo can be found everywhere.
Vodafone is fine, too, you won't notice any difference. T-Mobile's prepaid cards are called "Xtra", Vodafone's "CallYa".

The difference between using a US-based card and a German one are the costs (shown in US$ per minute):

T-Mobile US
- call US number from Germany: 1
- call German number from Germany: 1
- receive call from US in Germany: 1

German prepaid
- call US number from Germany: 3
- call German number from Germany: 0.40
- receive call from US in Germany: free

(The reason why you're charged for calls received from the US with your US plan is that the caller calls a number in the US and thus only pays for a call to the US. Someone has to pay for the redirection all the long way to Europe - that's you.
If you're using a German prepaid card the caller knowingly dials a German number and thus can be charged the full costs for the international call.)

So, a German prepaid card is only less expensive if you're mostly calling German numbers or want others to call you. Unfortunately, a German prepaid card costs about 30 US$, which might make the savings of a prepaid card less attractive. This literally counts twice since you're visiting two (or three) countries.

Last but not least: Using a public phone booth is way less expensive than any cell phone, even AT&T charges only 40 US-cent per minute for a call from Germany to the US, 60% off of the lowest cell phone tariff, others go as low as 3 cent.
Just enter "calling card" in your favourite search engine and you'll find plenty offers.

You'll need a Triband GSM Phone.
Verizon only sells CDMA, only a few companies such as T-Mobile sells GSM and CDMA phones, so before buying you'll have to check with your retailer.
T-Mobile is good, since you will not have to change your simcard.

hth