This will be like 75 percent business and 25 percent pleasure. I need some good calling cards or even voip for a month or so. Getting a plan is out of the question because I don't want to be tied up if I find the service bad or anything. Maybe buying a sim card is a good option if the rates for cell phone in Europe calling US and Asia is good.

I think your best bet would be to buy a cheap 'Pay as you go' phone in Europe. It would certainly work out cheaper than a US phone to US phone.
I did, the phone (Motorola) cost me €24, but I got €15 worth of free calls with it, so it was well worth it.

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Never make calls from your hotel room.
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You could go to internet-cafes or phone-shops which provide cheap international calls! You also can buy calling cards in this shops but which one is good depends on the country you are.
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Well, here in Belgium, there are night shops that sell calling cards. They give you 600 minutes for 5 euro. That's how I've been able to call my family for the past 5 months, I hope that helps.
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I think your best bet would be to buy a cheap 'Pay as you go' phone in Europe. It would certainly work out cheaper than a US phone to US phone.
I did, the phone (Motorola) cost me €24, but I got €15 worth of free calls with it, so it was well worth it.
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If cost is your number one worry then you can try a dial around service like Onesuite.com, you can use any local phone in Europe to call Onesuite access number then call the number in U.S. or what ever country you wish to call. They also have voip service so if you can connect to the internet then you may call also using Onesuite voip for like 2 cents per minute to U.S.
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you could buy a pay-as-you go SIM card and then use pre-dial numbers such as Telediscount:

http://www.telediscount.co.uk/

Calling cards are not really necessary since pre-dial numbers are just as cheap.

You could also buy a Skype mobile phone (also available with pay-as-you-go):

http://www.skype.com/allfeatures/3skypephone/

You cheapest option is taking a laptop and finding a wifi hotspot. See:

http://www.fon.com/en/
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I also recommend Onesuite. You can use voip or phone card services with one single account meaning more options but less hassle on your part. Just sign up with Onesuite.com for a minimum $10 and you're all set. They have local access numbers in Europe for phone cards services and you can also use the voip feature as long as you can connect to internet.
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