Norwegian pre-paid GSM in German Phone
 

We have a basic pre-paid phone we purchased in Germany last year. We are returning later this month and will use the phone in Germany. We also will use the phone first in Norway, then Denmark and then Germany. We may also need the phone in Sweden, Belgium, Portugal, Spain and Italy. Should we purchase pre-paid GSM cards in several of the other countries or just add minutes on the German card? What is involved with purchasing a pre-paid GSM card in a country different from where we purchased the phone; how is the new card activated, etc? Thanks for any help

If the phone came bundled with a prepaid SIM card it very likely has a SIMlock and won't accept other SIM cards unless you get the phone unlocked. Except for that we have identical cell phone standards in whole Europe so there's a general compatibility between handsets and networks.
However there's no universal procedure on how to purchase and activate SIM cards - unless you are using a single SIM card and roam in these countries you will need to select a provider for each of these countries and find out where to buy them and how to activate them which can be a pain as you might be required to visit operators' shops to show your ID as part of the registration process. Also consider the costs of the SIM card itself and the minimum topup amount required. Depending on how long you'll stay that may not pay off.
Also be aware that in Europe you don't buy airtime volumes like in the US but here you simply top up amounts of money onto your prepaid account from which your usage will be deducted according to the valid price list.

As you seem to be new to this sphere, I think the most convenient way would be to purchase a toggle mobile SIM card from the UK which allows you to request a local number from most of the countries you are travelling to through their website (so-called "toggle countries" which include Germany, Norway, Denmar, Sweden and Spain). I don't want to go too deep into the technical details but once you have assigned a local number from a certain country to your toggle SIM card calls in that country become very cheap and you will also have a local number under which people from this country can reach you at domestic rates, even if you leave that country.
Most notably the US are also a toggle country, so you can request an American local number under which people can call you during your trip at domestic rates. While you are in the toggle countries you won't be billed for these incoming calls to any of the local numbers you have obtained and once you are in the other countries not counted as "toggle countries" (Belgium, Portugal and Italy) with some modest £0.04/min.
Outgoing calls to the US are charged with £0.03/min from toggle countries, however from the other destinations the rate of £0.75/min is very high - you should consider let people call you instead of placing outgoing calls in order to keep your bill low.

For more information about toggle please see the corresponding thread: http://www.prepaidgsm.net/forum/showthread.php?t=6765

Hi I would also consider a Piranha Sim, www.piranha-mobile.com as these come with local US numbers and very competitive rates.

Hi to the Ohio Valley.

I think to give you a decent advice of what to do, you have to state what you want to do with your European SIM: calls, texts, data? Any idea how much and where to?

1st you should find find out (as Inquisitor has said) if your device has a SIM-lock or not. This is kind of tricky in the US. If your phone has GSM on 850 Mhz or 1900 Mhz, you can put in any AT&T or T-Mobile US SIM card and check if it connects to an network. But with cheap phones from Europe, they often cover only the European bands of 900 and 1800 Mhz (check the specs).
Assuming that the phone is SIM-locked, you can only put in the SIM cards of the provider (or with a NET-lock) of the network operator. If you can't get it unlocked, check if the given German provider has an EU package offer which might be the better deal, if you use it only lightly.
If it isn't locked or you find someone to unlock it (ask around in the "independent cell phone stores" run by immigrants in your country), you have the choice of adding new SIMs.
But have in mind that the 2 suggestions of Toggle Mobile and Piranha are only good for voice and text. It's a total different story if you want to use (a lot of) data and can channel your calls through VoIP (like Skype). For this, you should look at prepaidwithdata.wikia.com

If the phone has a SIMlock it will usually request an unlock code right after entering the SIM card's PIN code (or immediately if no PIN code is set on the SIM card), so you don't actually need to be in the coverage zone of a compatible network to see if there's a SIMlock. Just plug in any SIM card you have at hand.

more info please
 

Was your previous visit over a year ago? Do you remember what brand the SIM was? When you turn the phone on does it indicate 'no network found' [probably a European two band phone] or invalid SIM [a quad band phone, but the SIM is unrecognized by american networks].

For texts and voice Piranha & Toggle are two preferred choices. Piranha is easier to get shipped to the USA. Check Piranha's rates.