220 is a bit of a misnomer. I believe the US is actually 240V @ 60Hz while the EU standard is 230V @ 50Hz. From the internet:
However, if the equipment concerned operates on a compatible voltage, and if the equipment concerned is not sensitive to the different AC frequency, then you could connect a European device to an American supply.
To take one example, the main difference between an American domestic 240 V supply and a UK 240 V domestic supply is the grounding/earthing arrangement. In the US outlet both legs of the 240 V supply are hot and are 120 V from ground. In the UK 240 V supply one leg is live and one leg is neutral (close to earth potential). In other European countries the supply voltage and grounding arrangements may be different.
As mentioned by other posters, European devices are designed to operate safely in a variety of different supply situations with both supply legs fully isolated and insulated from exposed parts. So a European nominal 230 V device can be plugged into a US 240 V socket without problems.